Donald Trump had a good night on March 15, but polls show Republican party isn't entirely behind the GOP front-runner. (Peter Stevenson/The Washington Post)

Two groups leading the charge against Republican front-runner Donald Trump vowed to soldier on after his latest primary wins even as many senior party figures and donors retreated to the sidelines Wednesday, struggling to take stock of the careening presidential contest.

As Trump’s delegate lead expanded, there were signs of further polarization within the party. Florida Gov. Rick Scott urged Republicans to unite behind the billionaire developer and begin preparing for the general election. Meanwhile, South Carolina Gov. Nikki Haley, a top surrogate for former candidate Marco Rubio of Florida, told reporters Wednesday that she was “privately praying” for Sen. Ted Cruz of Texas to win the nomination, though she stopped short of formally endorsing him.

“My hope and my prayer is that Senator Cruz can come through this and that he can push through and really get to where he needs to go, because we do want a strong leader, we do want somebody that’s conservative, we do want somebody that’s action-minded,” Haley said at a news conference in Columbia, S.C.

Sen. James M. Inhofe (Okla.), another Rubio endorser, decided to pass up his Senate colleague, Cruz, and endorse Ohio Gov. John Kasich. “Out of the three still in the race for president, John is my guy,” Inhofe said in a statement.

Leaders of the Stop Trump movement also said they would press on, hoping to prevent him from securing the nomination before this summer’s convention.

“You’re not the nominee until you get 1,237 delegates, and I don’t see how Trump gets there,” Katie Packer, the GOP strategist helping lead Our Principles PAC, said in an interview after Tuesday’s primaries.

Packer said supporters of the super PAC — which spent nearly $13 million on a barrage of hard-hitting anti-Trump ads — plan to confer over the coming days on its next moves. Among the issues under discussion are whether the group should continue to pursue a broad media strategy or focus more narrowly on delegates in the hope of swaying their votes if there are multiple ballots at the convention in Cleveland.

“We are going to continue to push forward,” she said.

Meanwhile, the conservative advocacy group Club for Growth, which together with its sister super PAC has put $8.5 million into anti-Trump spots, is spending $200,000 to air a new ad in Utah beginning Thursday that seeks to link the New York businessman’s position on health coverage with that of Democratic candidate Hillary Clinton. Utah holds its primary on Tuesday.

“In terms of the presidential race, the Club for Growth remains primarily focused on defeating Trump, who is the worst candidate in the GOP field on economic issues, and we continue to believe that Ted Cruz is the best in the field, by far,” said spokesman Doug Sachtleben.

Still, it’s unclear whether wealthy conservatives who have been backing the anti-Trump effort will want to put much more money into an ongoing campaign. Some top Rubio fundraisers — deeply disappointed by his exit from the race Tuesday after losing Florida — said Wednesday that they plan to stay out of the White House race for now.

Donald Trump will almost certainly be the delegate leader heading into July's Republican National Convention – but that doesn't mean he'll win the nomination outright. (Peter Stevenson/The Washington Post)

“It’s onto the next thing, and the next thing is to keep control of the House and the Senate,” said Virginia developer Bob Pence, who was set to host a fundraiser Wednesday evening for five members of Congress. “That’s what I view as my role for the rest of the cycle.”

North Carolina retail executive Art Pope said he was considering running to be one of the state’s delegates to the national convention, rather than work to raise money for another presidential candidate.

“The possibility of an open convention and the consequences are historic,” Pope said. “I have not given up on the Republican Party; that’s why I’m considering going as an uncommitted delegate, to see what I can do to help work things out.”

Others urged unity behind Trump.

“It’s time to get behind Donald and recognize that he brings something to the party that we’re lacking,” said Florida lobbyist Brian Ballard, who raised money for both Rubio and former Florida governor Jeb Bush, and represents Trump’s business interests in Florida. “I think we have to stop throwing rocks at one another and get comfortable with the idea of Donald Trump being our nominee.”

But there was little evidence of agreement among GOP leaders in Washington.

Rep. Jason Chaffetz (R-Utah), who campaigned actively with Rubio, said he received calls and emails from Cruz’s campaign on Tuesday night seeking his support ahead of Utah’s primary. But Chaffetz said he told them he would keep his powder dry for now.

“I intend to vote for the nominee, but I’m going to focus on doing what I was elected to do,” Chaffetz said. “The presidential race has its own trajectory. . . . Voters are smart enough to figure this out. It’s so late in the game, I don’t know that endorsements mean a hill of beans anyway.”

Trump was scheduled to speak privately by phone Wednesday with Sen. Orrin Hatch of Utah, the longest-serving Republican in the Senate. Hatch previously backed former Florida governor Jeb Bush, and then Rubio after Bush dropped out. But he said he has no plans to endorse anyone next.

“That’s the kiss of death, if I do it,” Hatch said. “I’ve been wrong twice now.”

Paul Kane contributed to this report.