Romney To Cross Delegate Halfway Mark As Pressure Builds On Rivals Mitt Romney will cross a symbolic threshold Tuesday in his quest for the Republican nomination, leaving his rivals with a tough choice -- wait at least until the end of April for the next chance to challenge him, or do as party leaders suggest and coalesce around the front-runner. The contests Tuesday in Wisconsin, Maryland and the District of Columbia -- which Romney could feasibly sweep -- will give Romney enough delegates to cross the halfway point toward the 1,144 needed to clinch the nomination. His opponents have said they do not intend to drop out until Romney actually reaches that target. Rick Santorum on Sunday vigorously warned the party against rushing to crown a nominee, invoking the drawn-out battle between Hillary Clinton and Barack Obama in 2008, which resulted in a strong nominee who won in November. However, the race between Clinton and Obama was much closer at this stage than the race between Romney and the rest of the field. Santorum -- not to mention Newt Gingrich and Ron Paul -- increasingly face doubts about their ability to topple Romney or even prevent him from reaching 1,144 delegates to force a convention floor fight. Campaigns cost money to run. Gingrich, for one, already has acknowledged his funding stream is starting to slow. Romney, recognizing the odds, abandoned his typically cautious tone Sunday evening and referred to himself as the likely nominee when discussing Democratic efforts to target the Republican candidate. And so he's going to try in every way he can to divert to some other kind of attack and try to have people disqualify our nominee, which will probably be me," Romney said. Indeed, top Obama administration officials -- including Vice President Biden and Secretary of State Hillary Clinton -- over the weekend trained their criticism on Romney, particularly his foreign policy positions. Top Republican leaders have endorsed Romney over the past week, including Florida Sen. Marco Rubio and Wisconsin Rep. Paul Ryan. And Senate Republican Leader Mitch McConnell, while not endorsing anyone, said in an interview Sunday that Romney is the likely choice so "it's time to turn our attention to the fall campaign" and make the case against Obama. According to the latest Associated Press count, Romney has 568 delegates. Santorum has 273, Gingrich has 135 and Paul has 50. If Romney's rivals choose to make the GOP nomination a fight to the finish, after Tuesday's contests they will have to wait until late April -- and possibly early May -- to have a shot at eroding his lead. Santorum is eyeing his home state of Pennsylvania, which holds its primary along with four other states on April 24, for his next big chance. The former Pennsylvania senator on Monday said he "absolutely" will win Pennsylvania. He said he might even eke out an "upset" in Wisconsin. "The establishment is trying to shove Mitt Romney down the throats of conservatives and Tea Party folks," he told Fox News. But the other April 24 contests are being held in the kind of New England and East Coast states, like New York and Connecticut, seen to be favorable territory for the former Massachusetts governor. Santorum, on "Fox News Sunday," said he was looking ahead to May -- when conservative states like West Virginia and Texas are voting. Santorum said he would keep going no matter how he performs in Wisconsin, which is seen as the battleground this Tuesday. Romney has led recently in the polls. Santorum warned the party Sunday against "cutting it short and getting the wrong candidate." He described the latest string of Romney endorsements as a sign the "establishment" is getting nervous. Speaking in Mishicot, Wis., Santorum suggested the show of financial strength on Romney's part is another sign the race should go on. Why is he spending $4 million in Wisconsin if the race is over -- if it's over and you know, there's no chance, then why is he bothering even campaigning anymore if it's over? Santorum said.