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Donald Trump has summoned a tornado of negative stories that threaten to rip his campaign from its foundation if he doesn't stop, supporters inside and outside Trump's orbit are warning.

Several top backers — including Republican National Committee Chairman Reince Priebus, former House Speaker Newt Gingrich and former New York Mayor Rudy Giuliani — are trying to persuade Trump to move past his feud with the parents of the late Iraq War soldier Humayun Khan, stop bashing fellow Republicans like House Speaker Paul Ryan and Sen. John McCain, and refocus his attacks on Hillary Clinton.

But hopes aren't high among Republican allies that Trump, 70, can make such a fundamental change at this point. And the Trump campaign publicly denies that any intervention is occurring at all.

"The reality is that I don't think anyone has any influence" over Trump, a party source told NBC News.

Within the GOP, strategists are increasingly wondering at what point candidates will aggressively break with Trump or the party will divert resources from the presidential race to head off a collapse down the ticket.

"They don't want to, but he's forcing people's hands," GOP strategist Ryan Williams told NBC News. Williams described the campaign as "free-wheeling and careening from one self-inflicted controversy to another."

Trump's allies within the party can complain, but they can't say they weren't warned.

Trump has made outrageous and offensive statements from the minute he announced his campaign last year, and he slimed Republican rivals at every step along the way.

He's resisted previous entreaties from party elders to change course after calling Mexican immigrants "rapists," proposing a ban on Muslim visitors to the United States, linking Sen. Ted Cruz's father to the John F. Kennedy assassination and bringing up a federal judge's "Mexican heritage" as proof of bias.

"He lacks any kind of self-control," a GOP operative said. "That's not my opinion. It's well demonstrated."

As Trump regularly reminds voters at rallies, however, he's also survived numerous so-called crises to reach his current position. But the general election isn't the primaries, and the timing and intensity of the current episode stand out.

CNBC's John Harwood quoted an unnamed ally of campaign manager Paul Manafort on Tuesday night who called the mood "suicidal" and said Manafort was "mailing it in" after concluding that Trump was incapable of taking his advice.

Another source inside the campaign told NBC News that Harwood's account was "all true" and that the environment was "way worse than people realize."

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Lending particular urgency to this week's chaos is Trump's declining position in the polls against Clinton, who appears to be enjoying a major bump from last week's Democratic convention.

Surveys indicate Clinton not only eliminating Trump's gains from his own convention, but also regaining the solid lead she held before FBI Director James Comey's criticism of her email practices depressed her support.

The most recent NBC News/SurveyMonkey poll puts him behind Clinton, 50 percent to 42 percent, with registered voters. A Fox News poll released Wednesday gave Clinton a 49 percent-to-39 percent lead.

Convention bounces are sometimes fleeting, but once the race settles, there are few opportunities for candidates to make up ground, making Trump's missteps especially dangerous.

The Olympics begin this weekend, making it harder for Trump to win free media for much of the month. He could make it up by buying TV time, but the Clinton campaign and allied groups have reserved $98 million in ads through November — compared to less than $1 million on Trump's side.

The less likely Trump looks to win and the more toxic he looks with key voting groups, the more pressure Republican candidates in competitive races will face to denounce him."

"If Trump wants us to make a choice between our senators and representatives and him, it won't be him," another GOP operative in a swing state told NBC News.

But it's a delicate balance. If Republican candidates abandon Trump en masse, party operatives warn, depressed voters might stay home and leave federal and state candidates vulnerable to an electoral wipeout.

While Republican candidates in some swing states have polled ahead of Trump by distancing themselves from his more controversial positions, they still need conservatives to show up and split their ticket to prevail.

So far, few high-profile Republicans running for office have repudiated Trump — even Sen. Kelly Ayotte of New Hampshire is sticking by him, despite Trump's recent insults and Ayotte's longtime discomfort with his rhetoric.

The further Trump sinks, however, the harder it becomes to hold everyone together.

A veteran GOP strategist suggested that the party should be able to win competitive House and Senate races with smart campaigns if Trump is trailing Clinton by 1 to 5 points. But if he starts to trail by double digits in polls — as he did in Fox's survey — it could create a panic as Republicans rush to disavow his candidacy in the hope that they might survive the coming disaster.

Publicly, Trump and his top aides argue that talk of campaign troubles are overblown."We're great — it's a terrible week for Hillary Clinton," campaign spokesman Jason Miller told NBC News with a smile Wednesday.

Trump, Miller said, has always been the anti-establishment candidate. His refusal to support Ryan against a pro-Trump primary opponent only reinforced that brand.

And the campaign has had some good news mixed with the bad. This week, it raised an impressive $80 million in campaign contributions along with party allies — short of Clinton's $90 million, but a strong improvement for a campaign that built its fundraising operation from scratch after Trump largely self-funded during the primaries.

Some also note that Clinton and other Democrats are vulnerable to negative stories.

The Wall Street Journal reported Wednesday that the Obama administration shipped $400 million in cash to Iran as part of a deal over sanctions at the same time Iran released Americans it had detained. The State Department said that the payment was unrelated and that the negotiations were kept separate, but Republicans accused it of paying a ransom.

Fact checkers have also pilloried Clinton this week for claiming that the FBI corroborated her previous defenses of her email practices.

But other campaign aides expressed concern that Trump failed to capitalize on Democratic weaknesses or emphasize his core strengths because he's too often distracted by side stories and settling scores within the GOP.

"We've got to get back to these basic issues that got him this far," former Trump adviser Barry Bennett told MSNBC.

Trump's afternoon speech Wednesday in Daytona Beach, Fla., demonstrated the difficulty. He began with a long and focused recounting of the Iran story and Clinton's statements on her use of a private email server. He also praised Sen. Marco Rubio for endorsing him, extending an olive branch to a onetime critic after having baited Ryan and McCain the day before.

"The campaign is doing really well," Trump said. "It's never been so well united."

But the usual Trump, still nursing past grudges and falling into bizarre tangents, wasn't far behind.

After discussing Iran, he turned to his old feud with Megyn Kelly, in which he said the Fox News host had "blood coming out of her wherever." Trump, who made the initial comment one year ago this week, told the crowd that "perverted" Democrats wrongly portrayed it as a comment on menstruation in attack ads, when, in fact, he meant "her nose, her ears, her mouth."

Despite his outward confidence, Trump has sounded more concerned about his position. In several interviews and speeches, he's made unsubstantiated claims that the election could be "rigged" against him, raising concerns that he might be laying the groundwork to delegitimize a Clinton presidency after a loss.

"Wouldn't that be embarrassing, to lose to Crooked Hillary Clinton?" Trump said in Florida. "That would be terrible."