David Jackson

USA TODAY

WASHINGTON — One way or another, Republicans are looking at the distinct possibility they will enter the fall election as divided as they have been in more than a half-century.

All thanks to Donald Trump and his many conservative critics.

If Trump goes on to claim the Republican presidential nomination, he may well face opposition from prominent party members ranging from 2012 presidential nominee Mitt Romney to current lawmakers to large groups of policymakers.

If rivals somehow manage to deny Trump the nod, Republicans would likely face the wrath of voters who have backed the brash billionaire in large numbers.

Threats included a rancorous July convention in Cleveland and continued party in-fighting that will undermine Republican candidates for the White House, Senate and House this fall.

"You have Democrats treating each other with kid gloves, and Republicans pounding each other with boxing gloves," said Republican pollster Frank Luntz. "It's not going away anytime soon. In fact, it's getting worse over time."

Some Republicans are urging people to take a deep breath. Tensions are high now, but the party will eventually coalesce around a single nominee.

"I don't think there's anything wrong with drama and intrigue, and we've got plenty of that," said Republican National Committee chairman Reince Priebus, speaking on CBS' Face The Nation. Priebus said the party needs to get a nominee, "come together, and then take it to the Democrats — I think that we'll get there."

The GOP presidential contest remains unsettled after a series of weekend contests.

Texas Sen. Ted Cruz maintained pressure on Trump, scoring easy wins Saturday over the billionaire in the Kansas and Maine caucuses. Florida Sen. Marco Rubio, meanwhile, won Sunday's contest in Puerto Rico, his second win of the campaign.

Trump, who claimed weekend wins in Kentucky and Louisiana, decried suggestions by some Republicans that they should form a new third party if Trump prevails. Such a move, he said, would "make it impossible for the Republican candidate, on the assumption it’s me, to win."

He added, “As a party we should come together and stop this foolishness."

Both Trump and Cruz have called on Rubio and Kasich to withdraw from the race, but don't count on that happening anytime soon.

Rubio says he will beat Trump in Florida's March 15 primary in which 99 delegates are at stake. Kasich, the governor of Ohio, said he will win that state's 66 delegates in another March 15 primary.

Florida and Ohio are both "winner-take-all" primaries, meaning the results could solidify Trump's hold on the nomination or throw the entire race into more confusion, increasing the chances of a contested convention.

Poll: Trump, Clinton have big leads in Michigan primaries

Both Trump and Cruz have warned of a revolt if Washington elites are seen as manipulating the convention to install their preferred candidate.

There hasn't been a contested convention since the Republican conclave of 1976, when conservative insurgent Ronald Reagan narrowly failed to defeat incumbent President Gerald Ford.

This year, signs of Republican discord are all around. Romney, the party's 2012 nominee, has said he will not support Trump if he is nominated, calling him dangerous for the country. His speech denouncing Trump won applause from Sen. John McCain of Arizona, the 2008 nominee.

More than 70 Republican foreign policy analysis have signed an open letter opposing Trump, saying his vow to re-make trade agreements will lead to economic disaster and his aggressive foreign policy plans will make the nation less safe.

Trump, meanwhile, has suggested he could still run third-party if he is denied the nomination, or if he feels the party is somehow not respecting him enough.

While Cruz is Trump's closest competitor, many Republicans also dislike him and fear that the abrasive Texas senator would also drag the party down to defeat in congressional and state races.

Political analysts said the Republicans may be looking at their worst split since 1964, the year that conservative nominee Barry Goldwater drew opposition from moderate Republicans (including Romney's father, Michigan Gov. George Romney).

David Axelrod, a longtime political adviser to President Obama who has made the '64 analogy, said Democrats should not celebrate too much at the GOP's troubles, even if Trump is the nominee.

"Trump has defied conventional wisdom throughout," Axelrod said. "He is willing to go with his attacks where no one else would and, left alone, will play the entire game on his opponent's side of the field."

One former Republican presidential candidate, Steve Forbes, predicted that Republicans would ultimately unite because at least one candidate will put together a solid program of issues and win a race that has too often been dominated by personality.

"What looks like a food fight is going to morph into something more positive," Forbes said.

Otherwise? "If the present course continues, you're going to have a fractured party," said the chairman and editor-in-chief of Forbes Media.

The Republican race has been a rough one. Candidates have swapped accusations of lying, the debates have been contentious shout-fests, and arguments have even centered on the size of candidates' various body parts.

Luntz, who has been conducting a series of focus groups, said it may not be easy for the Republicans to come together because the campaign dispute has gone beyond ideology: It's been personal.

"Ideological differences can actually be mended over time," Luntz said. "Personal differences are deeper, and they last longer."