(CNN) Sen. John McCain announced Friday in a statement that he cannot "in good conscience" vote for the GOP's latest plan to overhaul Obamacare, likely ending Republicans' latest effort to repeal and replace the Affordable Care Act. 
 
 "I cannot in good conscience vote for the Graham-Cassidy proposal," the Arizona Republican said in a statement. "I believe we could do better working together, Republicans and Democrats, and have not yet really tried. Nor could I support it without knowing how much it will cost, how it will (affect) insurance premiums, and how many people will be helped or hurt by it. Without a full CBO score, which won't be available by the end of the month, we won't have reliable answers to any of those questions." 
 
 McCain's "no" vote means it is likely Republicans won't be able to repeal and replace Obamacare before September 30, as Sen. Rand Paul of Kentucky said he would not back Graham-Cassidy and Sen. Susan Collins of Maine has said she is leaning "no" on the proposal. But there are still questions as to where Alaska Sen. Lisa Murkowski is at the moment. It's also unclear if senators on the fence would support a procedural motion on the bill even if they decide they are against Graham-Cassidy in the end. 
 
 Republicans need at least 50 votes to pass the measure under the process of reconciliation. 
 
 Murkowski, Paul and Collins also under scrutiny 
 
 McCain was one of three most-watched members on the fence and considered a key vote on the bill. Without his support, Republicans would need to get Murkowski as well as Collins to sign on. It's unlikely considering the fact that Collins said Friday afternoon that she was leaning against the bill and had key concerns that the legislation did not do enough to protect individuals with pre-existing conditions. 
 
 "I'm leaning against the bill," Collins said Friday at a Portland, Maine, event, according to The Portland Press Herald. 
 
 A Republican aide involved in the process said Friday afternoon that GOP leaders are at the "evaluating options" stage right now. 
 
 The aide added, "I'm not breaking news telling you this isn't good." 
 
 Paul, the only other Republican other than McCain who has so far definitively come out against Graham-Cassidy, is "unlikely" to change his mind even if changes are made to the bill, his spokesman Sergio Gor told CNN. 
 
 Graham and McCain's close friendship 
 
 McCain's announcement comes despite that one of the bill's key sponsors -- Sen. Lindsey Graham of South Carolina -- is a close confidant. The thinking was if anyone could convince McCain to vote "yes," it would be Graham. 
 
 "I take no pleasure in announcing my opposition. Far from it," McCain said. "The bill's authors are my dear friends, and I think the world of them. I know they are acting consistently with their beliefs and sense of what is best for the country. So am I." 
 
 McCain has said for weeks that he would not support health care legislation that had not gone through "regular order," meaning Senate hearings, an amendment process and a rigorous floor debate. 
 
 Graham said he "respectfully" disagrees with McCain and will "press on" with his legislation. 
 
 "My friendship with John McCain is not based on how he votes but respect for how he's lived his life and the person he is," Graham said in a statement and on Twitter, adding later, "I feel an obligation to fix this disaster and intend to push forward for state-centric health care versus Washington-knows-best health care." 
 
 My friendship with @SenJohnMcCain is not based on how he votes but respect for how he's lived his life and the person he is. — Lindsey Graham (@LindseyGrahamSC) September 22, 2017 
 
 McCain voted "no" on the last health care proposal in July for the same reason. McCain's dramatic floor vote, which happened just weeks after he was diagnosed with brain cancer, came in the early morning and was captured as one of his most "maverick" moments in the Senate. 
 
 What the White House is thinking 
 
 A senior White House official told CNN that McCain's opposition "undeniably hurts" the effort to repeal and replace Obamacare but that President Donald Trump is not ready to give up on the effort yet. 
 
 "The President has been engaged all along, and I think you will continue to see him reach out," the official said. "We have been having conversations with Graham and Cassidy for a couple months and ... even though there may be members who want to give up, the President does not." 
 
 Top White House aides have been talking with Graham and Sen. Bill Cassidy for months now, and in between events at the United Nations this week, Trump called senators to talk about the upcoming health care vote, White House officials said. Trump was hoping to solidify Republicans around the deal struck by the two senators and urged many of the lawmakers to stay loyal to him. 
 
 The White House official, though, added that even though chances of passing health care look bleak, the White House intends to juggle between Graham-Cassidy and tax reform next week. 
 
 Vice President Mike Pence indirectly addressed the decision during a speech Friday afternoon in Anderson, Indiana. 
 
 "The vote could come as early as next week and this is not going to be easy. Even now, the opposition is forming up and some have gone so far to announce their opposition already. But President Trump and I are undeterred," Pence said. 
 
 "We cannot in good conscious abandon this cause," Pence said to applause in his home state. 
 
 Democrats praise McCain 
 
 Just moments after McCain announced his opposition, Democrats seized on the opportunity to bring back bipartisan talks that had stalled last week. 
 
 Democratic Sen. Patty Murray of Washington and Republican Sen. Lamar Alexander of Tennessee had held bipartisan hearings over the last month on how to stabilize Obamacare marketplaces and were making progress in their negotiations. But the House leadership made it clear last week that the chamber probably would not be able to pass such a bill. 
 
 As soon as McCain announced his opposition, Murray announced she was still open to reigniting those talks. 
 
 "I agree with Senator McCain that the right way to get things done in the Senate — especially on an issue as important to families as their health care — is through regular order and working together to find common ground," Murray said. "I'm still at the table ready to keep working, and I remain confident that we can reach a bipartisan agreement as soon as this latest partisan approach by Republican leaders is finally set aside." 
 
 Senate Minority Leader Chuck Schumer also praised McCain shortly after his announcement. 
 
 "John McCain shows the same courage in Congress that he showed when he was a naval aviator," the New York Democrat said in a statement. "I have assured Senator McCain that as soon as repeal is off the table, we Democrats are intent on resuming the bipartisan process." 
 
 For her part, House Minority Leader Nancy Pelosi said her members would continue working "to put the stake in the heart of this monstrous bill." 
 
 "This weekend, we will continue to highlight the devastating costs Republicans are trying to inflict on hard-working Americans," she said in a letter to colleagues. 
 
 This story has been updated and will update with additional developments. ||||| Sens. Susan Collins (R-Maine) and Rand Paul (R-Ky.) listed their concerns on Sept. 24 about a health-care bill sponsored by Sens. Bill Cassidy (R-La.) and Lindsey O. Graham (R-S.C.). (Bastien Inzaurralde/The Washington Post) 
 
 Sens. Susan Collins (R-Maine) and Rand Paul (R-Ky.) listed their concerns on Sept. 24 about a health-care bill sponsored by Sens. Bill Cassidy (R-La.) and Lindsey O. Graham (R-S.C.). (Bastien Inzaurralde/The Washington Post) 
 
 BREAKING: Sens. Bill Cassidy (R-La.) and Lindsey O. Graham (R-S.C.) will release a revised version of their health-care bill Monday aiming to send more health-care dollars to the states of key holdout Republicans. 
 
 The Cassidy-Graham bill overhauls the Affordable Care Act by lumping together spending on subsidies and Medicaid expansion and redistributing it to states in the form of block grants. Alaska would get 3 percent more funding between 2020 and 2026 and Maine would get 43 percent more funding during that time period, according to a summary of the revised legislation obtained Sunday by The Washington Post. 
 
 Republican senators from both states, Lisa Murkowski of Alaska and Susan Collins of Maine, have said they want to understand how Cassidy-Graham would affect their states before supporting the bill. Both have expressed deep opposition to cuts to health-care spending under previous versions. Independent analysts had estimated that both states would lose federal funding under the earlier Cassidy-Graham bill. 
 
 Arizona, where Republican Sen. John McCain has also indicated he may not vote for the bill, would see a 14 percent increase, according to the estimates. The estimates also take into account the amount of money states would save because they no longer have to match the expanded Medicaid program with any of their own dollars. 
 
 Three people with knowledge of the draft said Cassidy planned to unveil it Monday. 
 
 This story will be updated. 
 
 The floundering Republican attempt to undo the Affordable Care Act met hardening resistance from key GOP senators Sunday that left it on the verge of collapse even as advocates vowed to keep pushing for a vote this week. 
 
 With party leaders just one “no” vote away from defeat, Republican senators from across the political spectrum distanced themselves from the plan written by Sens. Bill Cassidy (R-La.) and Lindsey O. Graham (R-S.C.). They voiced opinions ranging from measured skepticism to outright hostility toward a proposal that had already been trending toward failure over the past three days. 
 
 The fresh discord over a signature Republican promise added turbulence to the start of a critical week for President Trump and Senate Majority Leader Mitch McConnell (R-Ky.). In addition to health care, both are watching Tuesday’s special-election primary runoff in Alabama, a high-stakes intraparty fight between establishment Republicans and conservatives that could set the tone for the midterm elections next year. GOP leaders also are expected to unveil their most detailed blueprint yet of tax cuts they hope to pass by the end of the year. 
 
 [The Cassidy-Graham bill probably won’t become law. And more than half of America is good with that.] 
 
 “Eventually we’ll win, whether it’s now or later,” Trump said of the health-care effort Sunday as he prepared to board Air Force One to return to Washington after spending the weekend at his golf resort in Bedminster, N.J. 
 
 Sen. Susan Collins (R-Maine), a moderate Republican who has opposed previous efforts that cut Medicaid and eased coverage ­requirements, said in a TV interview that it was “very difficult” to envision herself voting for the health-care bill. 
 
 Sen. Ted Cruz (R-Tex.), a conservative who has advocated a more far-reaching repeal of the ACA, commonly called Obamacare, said he and at least one other conservative colleague do not back the measure “right now.” 
 
 And Sen. Rand Paul (R-Ky.), who has stated definitively that he opposes the current measure, showed no signs of backing down without dramatic changes to the bill’s core approach that probably would come at the cost of other Republican votes. 
 
 Graham and Cassidy pledged to keep trying to pass their bill — but the White House and McConnell gave differing accounts of the path ahead. White House legislative affairs director Marc Short predicted a Wednesday vote, while a McConnell spokesman declined to publicly embrace that timeline. 
 
 Speaking on CNN’s “State of the Union,” Collins cited concerns about how the Cassidy-Graham legislation would affect Medicaid recipients and people with pre­existing medical conditions, among other things. 
 
 [Two-thirds of Americans think Trump is dividing the country — including a fifth of his supporters] 
 
 “It is very difficult for me to envision a scenario where I would end up voting for this bill,” Collins said. “I have a number of serious reservations about it.” 
 
 Collins voted against a repeal bill in July, and she is a key vote in the current dynamic. She said she chatted at length with Vice President Pence on Saturday, but it wasn’t enough to sway her. She said she wants to see the limited analysis due out this week from the nonpartisan Congressional Budget Office before making a final decision. 
 
 Two Republican senators — Paul and John McCain (Ariz.) — have already said they will vote against Cassidy-Graham. A third would be enough to defeat the bill, since no Democrats are expected to support it. Republicans hold a 52-48 advantage in the Senate and can lose only two votes from their own party and still pass legislation with the help of a tiebreaking vote from Pence. 
 
 Trump said Sunday that the senators opposed to or leaning against voting for the bill, including McCain and Collins, would benefit from the block grants included in the proposal. 
 
 “Every state you’re talking about, it happens to be particularly good for,” Trump said. 
 
 The bill has been roundly rejected by influential national groups representing physicians, hospitals and insurers. Over the weekend, six such organizations, including the American Medical Association and the American Hospital Association, issued a joint statement urging the Senate to reject the measure. 
 
 While the CBO plans to release a “preliminary assessment” early this week, officials there have said they will not be able to provide estimates of how Cassidy-Graham would affect insurance premiums or the number of people with coverage “for at least several weeks.” Trump and McConnell are trying to bring the bill to a vote by the end of this week to take advantage of a procedural rule allowing the plan to pass with just 51 votes. 
 
 It remained far from clear Sunday that they could get even close to that number. 
 
 Addressing Cassidy-Graham at the Texas Tribune Festival in Austin, Cruz said: “Right now, they don’t have my vote. And I don’t think they have Mike Lee’s either,” referring to one of Utah’s senators. 
 
 Cruz said that he and Lee met with Graham and Cassidy last week to propose changes to the measure that would get them to yes. Their changes were not included in the latest draft. 
 
 Conn Carroll, a Lee spokesman, said Sunday: “We want some technical changes. We are working with Cassidy, but we haven’t committed to anything yet.” 
 
 Graham and Cassidy appeared on ABCs “This Week with George Stephanopoulos,” where they defended their plan and vowed to keep up their efforts to shepherd it to passage. 
 
 “We’re moving forward. And we’ll see what happens next week. I’m very excited about it,” Graham said. 
 
 The South Carolina Republican mentioned Collins and Paul as he made his pitch. “Rand Paul objects to the taxes,” he said. “But when you look at the bill, Rand, we save a lot of money over time for Medicaid. We put a cap on Obamacare growth.” 
 
 Paul said in a Sunday interview that he broadly opposes a keystone of the Cassidy-Graham plan: turning funding for the ACA into block grants for states. 
 
 “The problem I have with block grants is that looks like I’ve affirmatively said I’m okay with 90 percent of Obamacare as long as we reshuffle it and give it to Republican states,” he said. “That’s a horrible message.” 
 
 Paul said he is willing to listen to suggestions about how that element of the bill could be constricted. “Would I talk to them if they said they wanted to make the block grants half as much? I might,” he said. 
 
 Paul presents another challenge as well: Winning him over would probably alienate Republican senators who oppose a more aggressive repeal. That left GOP leaders no better off in their quest to secure enough Republican votes to pass Cassidy-Graham. 
 
 The proposal, which would also dramatically cut Medicaid spending over time, has drawn concerns from Republicans from states that have expanded Medicaid under the ACA. In an interview on CBS’s “Face The Nation,” Sen. Cory Gardner (R-Colo.), whose state expanded Medicaid, said he needs more information before he will take a position. 
 
 “I think the CBO will have a role to play in this,” Gardner said. “I believe there’s information that will be coming through a committee hearing on Monday and additional text changes that will add additional information.” 
 
 McConnell is also keeping a close eye this week on the Senate race in Alabama, where Republican Sen. Luther Strange is trying to get past insurgent primary challenger Roy Moore, a controversial but popular former judge. Trump and McConnell both back Strange, but supporters and associates of Trump, including former chief White House strategist Stephen K. Bannon and Housing and Urban Development Secretary Ben Carson, have praised Moore. 
 
 A Moore victory would be a blow to both McConnell and Trump, who have put their powerful political operations behind Strange. Some Republicans also say that outcome would embolden conservative insurgents to challenge other Republican senators in 2018. 
 
 Also this week, the “Big Six” negotiators from the White House, the Senate and the House are expected to unveil more details of their tax overhaul plan, which, like the health-care talks, could spark messy disagreements among Republicans. 
 
 Some of the elements of the plan have already started to take shape. Republicans are targeting a corporate rate of 20 percent in their overhaul, according to three people familiar with the emerging blueprint — a number that represents a substantial cut from the current 35 percent rate but falls short of the 15 percent Trump has advocated. 
 
 But for Senate Republicans, the first order of business this week is resolving the health-care push, one way or the other. Even the bill’s champions have started pondering the prospect of failure. 
 
 Asked on “This Week” what he will tell people if he comes up short, Graham responded: “That I did everything I could to get money and power out of Washington to give you better health care closer to where you live, and I’m not going to stop fighting.” 
 
 He also held up the possibility of using health care as a negotiating tactic in future legislative talks. 
 
 “I’m on the Budget Committee,” Graham said, adding, “we’re not going to vote for a budget resolution that doesn’t allow the health-care debate to continue.” 
 
 Robert Costa and Carol Morello contributed to this report.
– The latest Republican effort to repeal the Affordable Care Act may very well be dead after Sen. John McCain announced his opposition to it Friday, the AP reports. "I cannot in good conscience vote for the Graham-Cassidy proposal," CNN quotes McCain as saying in a statement. "I believe we could do better working together, Republicans and Democrats, and have not yet really tried." This would be the second time McCain has put a nail in the coffin of Republican efforts to end ObamaCare. McCain said he couldn't vote for the Graham-Cassidy bill without a CBO score, which wouldn't be available until later this month, to let him know "how much it will cost, how it will affect insurance premiums, and how many people will be helped or hurt by it." Republicans could only afford to have two senators side with Democrats in opposition to the bill. Sen. Rand Paul was already opposed and Sen. Susan Collins was leaning that way. A recent poll found only 24% of Americans support the Graham-Cassidy bill and 50% disapprove of it, the Hill reports.