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Washington (CNN)Shortly before Sen. John McCain entered the Senate chamber in the wee hours of Friday morning, reporters wanted to know how he'd vote.

He instructed them to "watch the show."

McCain killed his party's narrowly-crafted Obamacare repeal bill Friday not because he was opposed to dismantling the Affordable Care Act, but because he fundamentally believed the process -- the lack of hearings, the one-party, closed-door negotiations, the fact that in the end all that Republican senators could agree upon was a shell of the plan they'd promised -- was flawed.

Less than two weeks after surgery to remove a blood clot revealed McCain had brain cancer, the Arizona Republican -- still with a visible scar above his eye -- traveled 2,000 miles from Phoenix and returned to a hero's welcome Tuesday in the Senate, where he delivered an epic 15-minute speech that rattled the conscience of the body.

It was a fiery and intense lecture on the shortcomings of bypassing "regular order" and turning your back on compromise. But moments earlier, McCain had delivered a decisive vote to advance a health care bill that was still an uncertain product at that point, a kind of blessing for the type of secretive negotiations he'd just decried.

Photos:The life and career of US Sen. John McCain

US Sen. John McCain speaks at a town-hall meeting while campaigning for the presidency in 2008. He was the Republican Party's nominee for that year's election, which he lost to Barack Obama.

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Photos:The life and career of US Sen. John McCain

McCain sits on a sofa with his sister, Sandy, in a reproduction of a family photo taken around 1938. McCain was born in 1936 to Roberta McCain and John McCain Jr., a Navy admiral.

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Photos:The life and career of US Sen. John McCain

McCain sits with his grandfather and his father, both of whom were Navy admirals, in this family photo from the 1940s.

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Photos:The life and career of US Sen. John McCain

McCain, bottom right, poses with his Navy squadron in 1965.

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Photos:The life and career of US Sen. John McCain

McCain graduated from the US Naval Academy in 1958 and served in the Navy until 1981.

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Photos:The life and career of US Sen. John McCain

During the Vietnam War, McCain's plane was shot down and captured by North Vietnamese forces. Here, he is pulled out of a lake in Hanoi by North Vietnamese soldiers and civilians in October 1967. McCain broke both arms and his right knee upon ejection and lost consciousness until he hit the water. Upon capture, McCain was beaten, he has said. He was held for five years by the North Vietnamese and tortured.

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A Vietnamese doctor examines McCain in 1967. For his service, McCain was awarded the Silver Star, the Bronze Star, the Legion of Merit, a Purple Heart and the Distinguished Flying Cross.

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Photos:The life and career of US Sen. John McCain

A year after his release, McCain visits the Holt orphanage in Saigon, Vietnam, as a guest of the South Vietnamese government.

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Photos:The life and career of US Sen. John McCain

McCain, center, and his wife, Cindy, pose with US Rep. John Rhodes after McCain was elected to the House in 1982. McCain has represented Arizona ever since. In 1986, he became a US senator.

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Photos:The life and career of US Sen. John McCain

McCain talks with people in Hanoi, Vietnam, during the filming of the CBS special "Honor, Duty and a War Called Vietnam" in 1985.

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Photos:The life and career of US Sen. John McCain

Vice President George H.W. Bush re-enacts a Senate swearing-in with McCain and his family in 1986.

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Photos:The life and career of US Sen. John McCain

McCain, left, joins President George H.W. Bush at a news conference about soldiers missing in action during the Vietnam War.

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Photos:The life and career of US Sen. John McCain

McCain, bottom, attends a hearing of the Senate Ethics Committee in 1990. McCain was investigated as being one of five senators, called the Keating Five, who interfered with regulators on behalf of Charles Keating, a financier accused of financial violations and convicted of securities fraud. McCain was cleared, but the Senate Ethics Committee decided that McCain showed poor judgment in his efforts for Keating, who was a large contributor to McCain's campaign.

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Photos:The life and career of US Sen. John McCain

McCain gets a kiss from his wife as they kick off his campaign for the 2000 presidential election.

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Photos:The life and career of US Sen. John McCain

McCain spends time with his wife and children at their home in Phoenix in 1999. John and Cindy McCain have two daughters, Meghan and Bridget, and two sons, Jack and Jimmy. The senator also has three children from a previous marriage: Andrew, Douglas and Sidney.

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Photos:The life and career of US Sen. John McCain

McCain rests in a New Hampshire motel room while on the campaign trail in 1999.

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McCain poses with his wife and seven children in 2000. The children, from left, are Andrew, Jimmy, Jack, Bridget, Meghan, Douglas and Sidney.

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McCain laughs during an interview with "Tonight Show" host Jay Leno in 2000.

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McCain reaches out to supporters during a campaign rally in Portland, Maine, in 2000. He suspended his campaign several days later and eventually endorsed his primary opponent George W. Bush.

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Photos:The life and career of US Sen. John McCain

McCain addresses a shadow convention at the University of Pennsylvania in 2000. McCain was booed when he asked supporters to back George W. Bush for President.

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McCain and his wife host George W. Bush and his wife, Laura, at Arizona's Red Rock Crossing in 2000.

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McCain acts in a skit while hosting "Saturday Night Live" in 2002.

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McCain talks with US Marines in Iraq as he and other senators stopped at Camp Falluja in 2005.

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McCain and fellow US Sen. Hillary Clinton listen to President George W. Bush speak at the National Prayer Breakfast in 2007.

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Photos:The life and career of US Sen. John McCain

McCain, again running for President, speaks during a campaign rally in New York in 2008.

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McCain is introduced by retired Rear Adm. Tom Lynch before delivering a speech in Annapolis, Maryland, in 2008.

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McCain and his running mate, Sarah Palin, wave to the crowd at the Republican National Convention after he accepted the party's nomination in 2008.

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McCain shakes hands with US Sen. Barack Obama, the Democratic presidential nominee, before their first debate in 2008. Obama defeated McCain in the general election.

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McCain and US Sen. Mitch McConnell speak about health care reform in 2009.

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McCain gestures as he prepares to speak at the Republican National Convention in 2012.

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McCain listens as former FBI Director James Comey testifies to the Senate Intelligence Committee in June 2017.

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Photos:The life and career of US Sen. John McCain

US Sen. John McCain returned to the Senate floor in July 2017, less than two weeks after surgeons removed a large blood clot from his brain and diagnosed him with brain cancer. He received a standing ovation on both sides of the aisle.

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Photos:The life and career of US Sen. John McCain

McCain votes no on the GOP's "skinny repeal" health care bill in July 2017. He was one of three Senate Republicans who voted against the failed bill.

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McCain speaks to members of the media while heading to a roll-call vote in October 2017.

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McCain arrives for votes on Capitol Hill in November 2017. He suffered an Achilles tendon tear on his right side and has to wear a walking boot. In this photo, he's wearing the boot on his other leg. He said on Twitter that it was to give a break to his left leg, which was tired from compensating for his injury.

Friday morning, just before 2 a.m. ET, he delivered the fateful vote in the other direction. For over an hour, leadership tried to change his mind on the Senate floor on the "skinny repeal" bill. His junior colleague Arizona Sen. Jeff Flake appeared to be dispatched to talk him out of it. And when that didn't work, Vice President Mike Pence swooped in. Even President Donald Trump called to try a final "Hail Mary" to sway McCain, a source briefed on the call told CNN.

At one point, McCain was sitting with his long-time ally, Sen. Lindsey Graham of South Carolina. The two were deep in conversation as Graham nodded along. At one point Graham took a call, and the man who just days before had received an outpouring of support from his colleagues on the floor was all alone, with no Republican approaching the veteran senator.

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McCain has defied his party before. The former prisoner of war stood with Democrats to release a report on the use of enhanced interrogation techniques during the Bush years. He reached across the aisle to fix the country's health care system for veterans with independent Sen. Bernie Sanders, and was known to unload on his own party when he felt they needed a reality check.

But Friday's vote may be one of his most memorable moments. In the end, the senator voted against a bill that would have repealed the Affordable Care Act's individual and employer mandates, despised by Republicans, and against his party's seven-year campaign promise to dismantle President Barack Obama's signature legislative achievement. Instead, McCain took a vote that very well may re-chart the course of Trump's own legislative agenda.

Trump, of course, had insulted McCain back in 2015. "He is a war hero because he was captured," Trump said in a question-and-answer session in Iowa. "I like people that weren't captured, OK? I hate to tell you. He is a war hero because he was captured. OK, you can have -- I believe perhaps he is a war hero."

"So great that John McCain is coming back to vote. Brave - American hero! Thank you John," Trump tweeted.

McCain promised a show on the way in, and delivered. Reporters and observers in the gallery watched his every movement as he spoke to various senators. At one point, he even huddled with Democrats. As he was speaking to Senate Minority Leader Chuck Schumer and Sen. Dianne Feinstein, other Democrats came closer and closer, forming a large half-circle around the former Republican presidential nominee, who, make no mistake, has worked to thwart Democratic ambitions over the years as well.

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"John McCain is a hero and has courage and does the right thing," Schumer said afterwards.

Sen. Chris Coons, a Democrat from Delaware, had a feeling even earlier in the day that McCain may be on his side this time.

"We had a brief conversation that was intriguing and then several other senators also had other conversations with him. He was sort of leaving little hints, here and there," Coons said.

After the vote, Senate Majority Leader Leader Mitch McConnell lamented the end result -- McCain joining Republican holdouts Lisa Murkowski and Susan Collins in ending the Obamacare repeal dream for the moment.

"I regret that we're here," McConnell said. "I'm proud of the vote I cast tonight. It's consistent with what we told the American people we'd try to accomplish in four straight election if they gave us a chance."

As McConnell lectured his GOP colleagues for failing to uphold their promises to voters to end Obamacare, McCain sat nearby, hands folded in his lap, with Murkowski by his side, as she had been for most of the night.

Later, as he got into his car to leave the Capitol, McCain was asked, "Why did you vote no?"