Trailing in Wis., Santorum counts on Pa.

White House hopeful Rick Santorum said losing the Wisconsin Republican primary would not be do or die for him, but he has to win his home state of Pennsylvania. "We have to win Pennsylvania," the former U.S. senator from the Keystone State told NBC's "Meet the Press" Sunday. "And we're going to win Pennsylvania. I have no doubt about that." Santorum is statistically tied with front-running former Massachusetts Gov. Mitt Romney in a recent poll of likely Republican voters ahead of the April 24 Pennsylvania GOP primary. Santorum -- who told reporters last week he didn't think he would win the Wisconsin primary Tuesday, and then backtracked to say he thought he could win -- said Sunday "we're going to do very, very well" in Wisconsin. He is to spend Election Night in Mars, Pa., a borough near Pittsburgh with a population of 1,746, after campaigning for more than a week in Wisconsin, where he trails Romney by 5 to 10 percentage points in the polls. Romney, who is now directing nearly all his attack lines at President Barack Obama, is widely expected to expand his delegate lead Tuesday in Wisconsin, Maryland and the District of Columbia, where Santorum is not on the ballot. Wisconsin has 42 delegates at stake, Maryland has 37 and the District of Columbia has 19. Romney leads with an estimated 568 delegates to Santorum's 273. Romney told a pancake breakfast in Milwaukee Sunday Obama said he was "doing a great job -- not just a good job, a great job." "I wondered, is he that far out of touch with what the American people are feeling? The answer's yes," Romney said. Santorum remained adamant Sunday he wouldn't quit the race until Romney mathematically clinches the nomination with the needed 1,144 delegates, a total Romney analysts say is likely to achieve in early June. "If Gov. Romney gets that required number then, without a doubt ... if he's at that number ... we'll step aside," Santorum said on the CBS program. "But right now, he's not there -- he's not even close to it." Former House Speaker Newt Gingrich and Rep. Ron Paul of Texas also vowed Sunday to stay in the race. "We're not going to concede it to him," Gingrich said on CBS News "Face the Nation." He likened himself to the Kansas Jayhawks basketball team, which completed a come-from-behind win in the NCAA college basketball semifinals Saturday night. "I'm going to take Kansas as a model," he said. Paul said "obviously, yes," he was going to keep campaigning. "There is no way I'm going to quit speaking out," he told the CBS program. "I am trying to save the Republican Party from itself."