MIDDLETON, Wis. – Rick Santorum insisted Sunday that he would remain in the Republican presidential race for the long haul, defying mounting pressure from party elders to coalesce around front-runner Mitt Romney and focus on the fall contest against President Obama.

Santorum vowed to stay in the race until it is clear that the former Massachusetts governor has secured the 1,144 delegates required for the nomination, something that is unlikely until just about the end of the primaries in June.

As both men campaigned across Wisconsin on Sunday, it was Romney eyeing victory in this state’s Tuesday primary and Santorum looking ahead to his home state of Pennsylvania, where the former senator predicted a win that could reignite his insurgent candidacy.

Yet the chorus calling for Republicans to rally behind Romney grew louder Sunday. Senate Minority Leader Mitch McConnell, R-Ky., who stopped short of an official endorsement, said that Romney’s chances of winning the nomination are “overwhelming” and called on Republicans to turn their attention to the general election.

“I think it’s absolutely apparent that it’s in the best interests of our party at this particular point to get behind the person who is obviously going to be our nominee and to begin to make the case against the president of the United States,” McConnell said on CNN’s “State of the Union.”

And Romney’s support is growing beyond party establishment figures. Sen. Ronald Johnson, R-Wis., who was elected in 2010 as a political neophyte with a strong tea party following, endorsed Romney and campaigned with him.

“I just want to assure every conservative, I’ve spoken with Mitt, (and) I totally believe he is committed to saving America,” Johnson said as he introduced Romney at a pancake brunch in Milwaukee.

In a sign that party leaders are pivoting toward the general election, Johnson said on NBC’s “Meet the Press” that McConnell had tapped him to coordinate the party’s congressional agenda and message with the Romney campaign.

Santorum brushed aside such talk. “The establishment folks in Washington, D.C., they’re in the bubble and they see the world very, very differently than we do and I think most Americans do,” he told reporters.

Santorum’s day included another stop at a bowling alley, which has become his favorite new pastime, and lunch with his wife, Karen, and some family members in West Bend, Wis., where the menu included cheese curds and beer cheese soup.

Speaking at a Lincoln Day event in Fond du Lac, he tried to associate himself with Wisconsin Gov. Scott Walker, who is facing a recall election in June that is likely to become one of the most closely watched elections of the year.

At his campaign stops Sunday, Romney looked past Santorum and his other remaining Republican rivals and focused exclusively on the battle against Obama. At the pancake brunch, he attacked Obama for a “government-centered society” that he said would “transform America.”

“I don’t want to transform America,” Romney said. “I want to restore to America the principles that made us the hope of the earth.”

Romney was brimming with confidence as his motorcade made an unscheduled stop at a Culver’s restaurant off the highway. As they stood in line to order, Rep. Paul Ryan, R-Wis., explained to Romney the virtues of a “butter burger,” a favorite at the fast-food diner. Romney got one – and topped it off with fried cheese curds and a chocolate malt, paying for it with his platinum American Express card.