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TAMPA, Fla. — Donald Trump earlier this week promised to make Republicans “proud of our party and our movement.” Days later, he's punching up his message to skeptical party members: Get your act together.

“We have a war to win against a very crooked politician," he said at a rally in Tampa on Saturday, referring to Democratic rival Hillary Clinton. "I don’t want to waste a lot of time trying to defend ourselves against these phony (politicians)."

Republican U.S. presidential candidate Donald Trump gestures following a campaign rally in Tampa, Florida on June 11, 2016. SCOTT AUDETTE / Reuters

“The Republican Party has to come together, they have to get their act together,” he added, citing the potential for the next president to nominate multiple Supreme Court justices as the stakes in the race.

It’s a signal Trump’s rocky efforts toward GOP unification continue to stall as he faces persistent criticism from Republican leaders for racially-charged comments and a campaign operation that still seems ill-prepared for the general election.

The latest opposition to Trump’s candidacy came from former GOP presidential contender Mitt Romney, who on Friday told CNN he wouldn’t be voting for Trump, in part, out of a concern over the prospect for “trickle-down racism, trickle-down bigotry, trickle-down misogyny.”

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Those remarks seemed to rile Trump, who called Romney “choker” and a “stone-cold loser.”

Mitt Romney had his chance to beat a failed president but he choked like a dog. Now he calls me racist-but I am least racist person there is — Donald J. Trump (@realDonaldTrump) June 11, 2016

Referencing how Romney could mull the presidency after losing the White House in 2012, Trump said: “You go off into the sunset. You don't sit there jealous and sick to your stomach.”

While Trump spent some of his speech recycling his attacks against Clinton and the Obama administration — and even attacked Secretary of State John Kerry for being in a biking accident during Iran Deal negotiations — he spent a near-equal amount of time dismissing Republicans.

Supporters attend a campaign rally of Republican Presidential candidate Donald Trump at the Tampa Convention Center on June 11, 2016 in Tampa, Florida. Florida Gov. Rick Scott spoke at the rally and introduced Trump. Gerardo Mora / Getty Images

Trump also shrugged off the still-significant minority of senators that refuse to endorse him, saying it’s “fine” but added: “I’m saying, 'What the hell are they doing?'”

Trump said he just wouldn’t campaign for them, and warned they could have a “case where I win and many others don’t.”

“I would love to see the (Senate) majority, but the Republicans have to stick together, they have to be smart,” he said.

“I said, ‘Yes, I’ll apologize — to Pocahontas.' I’ll apologize, cause Pocahontas is insulted by this.”

The use of “they” for party-switching Trump — who was a Republican early on in life, before becoming a Democrat, then an Independent and then a Republican again — underscores lingering concerns for many Republican Party elders who don’t believe he represents them.

Such concerns have recently sparked fresh interest in the prospect of a dark-horse candidate taking the nomination away during the Republican National Convention next month.

But Trump seemed unconcerned with Republican Party skeptics, sticking to his usual freewheeling style despite recommendations from GOP leaders to reign it in now that he’s the presumptive nominee.

His current target on the trail has been Massachusetts Sen. Elizabeth Warren, whom he has called “Pocahontas” — a reference to controversy over her claimed Native American heritage. Trump said Saturday that he’d be willing to apologize — but not to Warren.

“I said, ‘Yes, I’ll apologize — to Pocahontas.' I’ll apologize cause Pocahontas is insulted by this, I think,” he said.

He also asked the crowd to shout out suggestions for his vice-presidential pick, and at one point thanked a few in the crowd for singing him “Happy Birthday” — but the billionaire businessman said he was torn about turning 70 on Tuesday.

"I don’t want to hear about that," he said. "I feel like I’m 35, that’s the good news."