CLEVELAND The Republican Party is at war with itself, and nothing that happens during the convention that will nominate Donald Trump for president is likely to change that.

The schism was on display on Monday, Day One of a convention among whose major themes are party unity.

The convention floor erupted in pandemonium as delegates for and against Trump engaged in a raucous war of words and chants, after the Trump campaign and the Republican National Committee used strong-arm tactics to defeat a delegate insurgency intent on derailing the New York businessman's nomination.

The rebellion never really stood a chance, but that it existed was fairly unprecedented.

Earlier in the day, Trump campaign chairman Paul Manafort and Ohio GOP Chairman Matt Borges skirmished over Gov. John Kasich's refusal to attend the convention. Manafort called Kasich, beaten by Trump in the primary, an embarrassment; Borges said Manafort doesn't know what he's talking about.

Both sides are crouched in their corners, unwilling to offer an olive branch to the other. Driving the division are sharp differences on key policy issues, and exactly what it means to be a Republican.

Trump and his populist wing are adamant that the celebrity real estate mogul earned the nomination where it counts the most: through the votes of millions of voters in a crowded, competitive primary contest. They want everyone else to fall in line.

Holdouts among the party's movement conservatives and establishment elders argue that Trump doesn't represent the core values of the party and behaves in a way that makes it near impossible for them to vouch for him as a viable president.

"This is a problem that has to be worked through," said Matt Schlapp, who as chairman of the American Conservative Union has put a lot of effort into trying to "harmonize" the populist and conservative wings of the party.

"I'm hopeful that most of the people not willing to support Trump will come to realize it's the right thing to do, even if it's in the privacy of the booth and not publicly," Schlapp added.

For Republicans, this intraparty arm wrestle is a real dilemma. Even Trump appears to recognize it. He cited party unity as a major reason he selected Mike Pence as his running mate. The Indiana governor is a classical Republican with close ties to the conservative movement. Republicans suspicious of Trump have hailed his selection.

Yet Trump, and his team, continues to antagonize his Republican critics, hardening their opposition.

Manafort, besides calling out Kasich, dismissed former presidents George H.W. Bush and George W. Bush, as well as former Florida Gov. Jeb Bush — whom Trump beat in the primary — as the Republican Party of the past. Ivanka Trump, Trump's daughter who is usually deployed to soften her father's rough edges, did the same in an interview with ABC News on Monday.

The Bush family and 2012 GOP nominee Mitt Romney headline the long list of prominent Republicans, both in office and out of office, who are staying away from Cleveland because of opposition to Trump. They include GOP senators running for re-election and a collection of Republican governors.

Their support, Manafort said, isn't necessary for victory over Hillary Clinton, the presumptive Democratic nominee.

"The party is unified," Manafort told reporters during a morning news conference. "The Bush family, while we would have liked to have had them, they're part of the past. We're dealing with the future. While we would like to have them, they do not reflect the broad strokes of the Republican Party."

Public opinion polls show a tight race between Trump and Clinton, with the former secretary of state sporting a small but consistent lead. Polling averages put Clinton's advantage at 3.2 percentage points. In a country that is politically divided, party unity is essential to victory.

Disinterest among party insiders and grassroots activists could cost Trump badly needed resources to remain competitive in the fall. That's why a party that has to paper over its differences this week in Cleveland is significant, and should be concerning to the Trump campaign.

Voters don't take their cues from party bigwigs, especially in this election cycle. And as polls suggest, opposition to Clinton, if nothing else, is enough to keep Trump in the game. Yet even with Republican voters, Trump's support isn't where it needs to be for him to be positioned for victory in November.

Trump is viewed favorably by only 66 percent of Republican voters, well short of the 90 percent rating, if not higher, that he needs to achieve to compete with Clinton. In the last month, the percent of Republicans unsatisfied with Trump as their nominee has spiked 8 points,\ to 60 percent.

By Election Day 2012, Romney's approval number with Republicans was over 90 percent.

"Trump just isn't going forward. He's still trying to coalesce Republicans," said Stuart Stevens, a fierce Trump critic and Romney's chief consultant four years ago. "At some point, they're going to wake up and realize they need Republicans more than they need him."

The root of the Republican family feud is a clash of ideology and style.

Trump is a populist. His foreign policy is quasi-isolationist, his trade policy is protectionist and he opposes reforming entitlement programs like Medicare and Social Security.

That runs counter to a Republican Party that has traditionally supported robust U.S. leadership abroad, backed free trade agreements and sought to reduce the size and scope of government, in part through the overhaul of Medicare and Social Security.

Trump's blunt, aggressive campaign style, however, has been an equally motivating factor Republican opposition to Trump.

They didn't appreciate what they deemed to be his below-the-belt criticism of his Republican primary opponents. They were horrified by his racially charged criticism of a U.S. federal judge, and worry about the complimentary way he has discussed the leadership tactics of dictators and strongmen like Russian President Vladimir Putin.

Lori Hack supported Sen. Ted Cruz of Texas in the primary and was removed as an Arizona delegate when she refused to commit to supporting Trump in a vote of delegates on the convention floor. She said in an interview this week that despite her policy disagreements with Trump, her opposition to him runs deeper.

"I think Trump is poison. I think Trump is going to be a defining movement for the GOP," Hack said. "Even though on a policy standpoint, Cruz and Romney are kind of the opposite, Romney's a moral man. He's fit to be president."