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 he 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 (Ky.), who stopped short of an official endorsement, said 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 H. 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. Asked about the comments from McConnell that the party needs to bring the nomination battle to a close, Santorum laughed and said, “I’m encouraged by all of this. . . . We’ve got a lot of folks seemingly getting very, very nervous two days before the Wisconsin primary.”

Santorum was similarly dismissive about Johnson’s endorsement of Romney. “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. “And we’re going to continue to go out and try to elect conservatives to the presidency, and that’s what we’re focused on.”

Earlier, appearing on “Fox News Sunday,” Santorum sounded defiant. “We need a conservative,” he said. “We need someone who can be a contrast with ­Barack Obama, not the same old tired establishment person that’s going to be shoved down our throat.”

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, 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.

“Wisconsin is now in the vortex of the national election,” Santorum said. “You can show the rest of the country that here in Wisconsin, that what you’ve done here in this state not only is a marker for how states need to be run to get government under control and bring freedom back at the state level, but you can send that same signal in this Republican primary to the entire country.”

But 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.

Earlier, Romney’s aides orchestrated an elaborate April Fools’ Day prank on him. They ushered him into a ballroom to give his stump speech. As he waited behind a black curtain, Ryan introduced him. The sound of applause played through the speakers, then Romney’s theme song, Kid Rock’s “Born Free.”

But when Romney stepped out from behind the curtain the room was empty, save for a few aides who were recording it on their iPhones.

“I got pranked upon,” Romney told reporters later. “This was classic.”