Republican presidential hopeful Mitt Romney campaigns in Wisconsin ahead of Tuesday's contests.

Story highlights

Voters in Maryland, Wisconsin and Washington, D.C., will cast ballots on Tuesday

Romney predicts a win in the much-watched Wisconsin primary

It takes 1,144 delegates to win the Republican presidential nomination

Santorum and Gingrich insist they will stay in until a candidate reaches that threshold

WASHINGTON CNN  — 

Consistently defiant rivals are doing little to hamper Mitt Romney’s momentum ahead of nominating contests on Tuesday in what is shaping up to be more of a general election fight between the former Massachusetts governor and President Barack Obama’s re-election team.

Rick Santorum and Newt Gingrich on Sunday insisted they will stay in the race until a candidate reaches 1,144 delegates – the necessary threshold to win the Republican presidential nomination – while acknowledging Romney currently has the advantage.

Santorum cited the Democratic nomination fight in 2008 and Mike Huckabee’s Republican presidential bid in 2008 to push back against the narrative the former Pennsylvania senator is hurting the party.

“Four years ago, everyone said, ‘Oh, we got to wrap this thing up’ and we did, and John McCain was the nominee. And Barack Obama and Hillary Clinton went in the summer and pounded it out,” the former U.S. senator from Pennsylvania said on “Fox News Sunday.”

“And guess what?” Santorum continued. “They came up with the best candidate, and we came up with someone who, well, just wasn’t able to win. We don’t need to repeat that again.”

Gingrich, the former House speaker, who scaled back his campaign infrastructure last week, said Sunday he is launching a come-from-behind strategy.

However, Romney’s competitors face a steep delegate climb.

Voters in Maryland, Wisconsin and Washington, D.C., will cast ballots on Tuesday and Romney is expected to win all three. There is then a three-week gap before the next set of elections.

Whatever the outcome Tuesday, Santorum said, he will not end his White House bid and instead will channel his energy into upcoming states that he said look “very, very good for us.”

However, if Romney reaches the necessary delegate threshold, both Santorum and Gingrich conceded they would end their campaigns.

“If Gov. Romney gets that required number, then without a doubt, if he’s at that number, we’ll step aside,” Santorum said on NBC’s “Meet the Press.” “Right now, he’s not there. He’s not even close to it.”

“Right now, he’s not there. He’s not even close to it.”

Wisconsin represents the latest showdown in the contest, with Santorum needing a victory to regain momentum against the growing Romney lead. A Romney triumph there Tuesday, which is expected, would further solidify his front-running status heading into the upcoming lull in primaries and increase pressure on Santorum and Gingrich to drop out.

The most recent poll from NBC News/Marist out of Wisconsin showed Romney with 40% support from likely primary voters, followed by Santorum’s 33%, Paul’s 11% and Gingrich’s 8%.

Over the weekend, Romney predicted a Wisconsin win based on support “growing stronger and stronger.”

“This was an uphill battle for me, if you look back three or four weeks ago, and now we’re looking like we’re going to win this thing on Tuesday,” Romney said in Fitchburg, Wisconsin, on Saturday. “I got a good boost from the folks in Illinois, and if I can get that boost also from Wisconsin, I think we’ll be on a path that will get me the nomination well before the convention.”

Tuesday’s votes follow a week of high-profile endorsements for Romney. He received the backing of U.S. Sen. Marco Rubio of Florida, former President George H.W. Bush, and Rep. Paul Ryan of Wisconsin, chairman of the House Budget Committee.

Their message: It is time to get behind one candidate to avoid harm to the party.

Ryan predicted the GOP campaign will effectively end if Romney sweeps Tuesday’s contests.

“If he gets a big delegate count, which I think he’ll get, then we believe, as conservatives, that we should coalesce around our nominee and focus on the task at hand, which is the fall election, and not drag this thing out, which I think becomes counterproductive,” Ryan said on CNN’s “State of the Union.”

Although he did not offer his official endorsement, Senate Minority Leader Mitch McConnell of Kentucky said Romney will be an “outstanding nominee.”

“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 “State of the Union.”

Sen. Ron Johnson of Wisconsin added his name to the growing list of Romney supporters Sunday and turned the conversation toward the general election.

“I’m looking forward to making sure that President Obama is a one-term president,” Johnson said on NBC’s “Meet the Press.”

The Obama administration took aim at Romney last week through surrogates, most notably Vice President Joe Biden, who accused Romney of being “consistently wrong” throughout his career as an investor, businessman, governor and presidential candidate.

On Sunday, Biden labeled Romney “a little out of touch,” pointing to his proposed policies on health care, the economy and the auto bailout.

“I can’t remember a presidential candidate in the recent past who seems not to understand, by what he says, what ordinary people are thinking about and are concerned about,” Biden said on CBS’s “Face the Nation.”

Romney continued to hammer the current White House occupant over health care and the economy, a theme echoed by Santorum and Gingrich to the Wisconsin Faith & Freedom Coalition on Saturday.

In a bit of April Fools’ Day fun Sunday, Romney’s staff set up a fake appearance in which Romney thought he would be addressing a campaign rally but walked out to find an empty auditorium except for staff members taping his reaction.

CNN’s Gregory Wallace, Ashley Killough and Rachel Streitfeld contributed to this report.