(AP) -- In a rare show of humility by the boastful billionaire, Donald Trump is acknowledging that his presidential campaign faces challenges and could ultimately fall short.

The Republican presidential nominee is straying from his signature bravado as he campaigns in the battleground state of Florida, even telling a gathering of evangelical ministers Thursday he's "having a tremendous problem in Utah." The same day, the reality show star acknowledged that his lack of political correctness could cost him the election if Americans reject his blunt approach.

"We're having a problem," Trump told the ministers, adding that the next president could get to nominate up to five high-court justices. "It could cost us the Supreme Court."

Trump's campaign planned to sit down with RNC officials in Orlando on Friday. But both Republican Party officials and Trump's campaign said the meeting was focused on Florida campaign operations and not tensions between the campaign and the GOP. The officials weren't authorized to comment publicly and requested anonymity.

After trouncing 16 challengers in the Republican primary, Trump is encountering worrying signs as his campaign moves into the general election. Democrat Hillary Clinton's lead over Trump in national polls has widened in recent days, while a growing number of fellow Republicans have declared they won't support their own party's nominee.

Trump's exercise in self-awareness is a marked departure from his usual tenor on the campaign trail, where for months at rallies he would tick through poll numbers showing him winning as if they were sports scores of his favorite team.

"We're going to win so big," Trump told a roaring crowd one month ago at the Republican National Convention.

Yet on Thursday, Trump was reduced to citing a poll that actually showed him a few points behind Clinton and arguing the race between them was close. Asked how he planned to reverse Clinton's advantage, Trump said he simply planned to do "the same thing I'm doing right now."

"At the end, it's either going to work, or I'm going to, you know, I'm going to have a very, very nice, long vacation," Trump told CNBC.

Even while working to restore confidence in his campaign, Trump appeared to court controversy anew when he said late Thursday that he was open to trying Americans suspected of terrorism at the Guantanamo Bay detention center in Cuba. Asked specifically about U.S. citizens, Trump said he didn't like that President Barack Obama and others wanted to try them in traditional courts rather than military commissions at Guantanamo Bay.

"I would say they could be tried there," Trump said. "That'll be fine."

In Utah, typically a reliably Republican state, Trump's challenges have been particularly striking. The state's large Mormon population has voiced serious skepticism about Trump, though the state's GOP governor has endorsed him.

"We've really been given a false narrative," Trump said of his struggles in Utah.

Yet in other traditionally GOP-leaning states, like Arizona and Georgia, Republicans are concerned Trump's unpopularity could give Democrats an improbable victory. Those concerns are compelling enough that dozens of worried Republicans gathered signatures Thursday for a letter urging the GOP chairman to stop helping Trump and focus on protecting vulnerable House and Senate candidates.

Trump said he wasn't worried Republicans would cut him off -- and threatened to stop fundraising for the party if they do.

The billionaire real estate mogul's unusually candid reflections about the uncertainty of his electoral prospects come as he's struggling to keep the focus on his opponent -- Clinton -- and avoid distractions.

Earlier this week he caused a major stir with comments about the Second Amendment that were perceived as advocating violence against Clinton, then faced questions yet again after declaring Wednesday that President Barack Obama was the "founder" of the Islamic State group -- a patently false claim.

It's comments like those that Clinton has seized to try to contrast her "serious, steady leadership" with the more volatile approach she says Trump would take to running the country.

"I just do not think insults and bullying is how we are to get things done," Clinton said as she laid out her economic plan Thursday in Warren, Michigan.

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Associated Press writers Steve Peoples in Washington; Catherine Lucey in Warren, Michigan; and Jill Colvin in New Jersey contributed to this report.

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