WASHINGTON — “I’m not losing,” President Trump insisted in an interview on Sunday with the Fox News anchor Chris Wallace after being presented with the cable network’s latest poll, which showed former Vice President Joseph R. Biden Jr. with an eight-point advantage nationally.

The president, who often promotes poll numbers when they are favorable to him — and even regularly advertises what he claims is a “96% Approval Rating in the Republican Party” without citing any source for that questionable statistic — said the public polls that showed him losing were “fake in 2016, and now they’re even more fake.”

There aren’t many campaign metrics out there these days to buoy a president who loves to cite a record he has shattered. He hasn’t been able to pack a stadium with supporters since the beginning of the coronavirus pandemic, and Mr. Biden has out-raised him for two months in a row. Unlike Hillary Clinton’s slim lead in national polls four years ago, Mr. Biden has held a nearly double-digit lead in an average of polls for more than a month.

In response, the Trump campaign has highlighted the meaningless marker of “boat parades” as a measure of voter enthusiasm. The most recent shattered record Mr. Trump has touted online is a heat index. “We may have set a record for doing such an interview in the heat,” Mr. Trump tweeted Tuesday, referring to his outdoor interview with Mr. Wallace. “It was 100 degrees, making things very interesting!”

Meanwhile, his campaign and his top advisers have echoed his attempts to discredit public polls, in an effort to treat them, dismissively, as an extension of “the media.” The Trump team sent a cease-and-desist letter to CNN after it published a June poll that showed Mr. Trump losing to Mr. Biden. (The network said it stood by its poll.) And in a recent interview with Newsweek, the president’s son-in-law Jared Kushner, who is overseeing Mr. Trump’s campaign, dismissed public polling as “all b.s.”

Privately, aides said, Mr. Trump knows things aren’t looking good for him — he just thinks the public polls are overstating the situation. His campaign does not conduct national polls, but aides have presented him with internal data about battleground states that show a closer race than the public polling numbers. His pollsters tell him regularly that he is in a close race and that there is more polling bias in the news media today than there was four years ago, a claim untethered to any measurable metric. They assure him that his base is still enthusiastically engaged and that the middle that might have been planning to vote for him in March has moved away through no fault of his own.

That has helped lead Mr. Trump to think that the public polls are overstating Mr. Biden’s advantage, advisers said, and that they offer only a snapshot in time. But his internal numbers still show him trailing Mr. Biden, and he is worried about his standing. He asks his advisers with more regularity, “What do we need to do?” and grills his friends about “how is it looking?” while making public course corrections, the advisers said.

Over the past several weeks, he changed his stance on promoting masks, claiming that it was “patriotic” to wear one, and resuscitated the daily coronavirus news conference — both an acknowledgment that he needs to be seen as taking the virus seriously again.

On Tuesday evening, campaign aides circulated a news story from CNBC, in which the host Jim Cramer said that Mr. Trump’s belated endorsement of face coverings had sparked a rally in recovery stocks.

The president also unceremoniously demoted his longtime campaign manager, Brad Parscale, and his campaign has shifted the majority of its advertising resources to a message of law and order, claiming inaccurately in a new television ad spot that if Mr. Biden is elected, the country’s police departments will cease to exist.

His political opponents assume he knows he is losing, and badly, and that his blanket dismissal of public polling as “fake” is part of a strategy to sow doubt and confusion in November. “Saying the polls are fake helps in laying the predicate for claiming the election is rigged,” said William Kristol, the conservative writer and prominent “Never Trump” Republican. “Because his brand going forward depends on his being a victim of a rigged system, not accepting defeat. He has a general interest in discrediting the truth, and this is part of an assault on the truth.”

But aides said that even in private conversations, Mr. Trump has not let the reality of his current political standing fully sink in.

“No one’s ever come back from something like this,” said Lee Miringoff, director of the Marist College Institute for Public Opinion, referring to Mr. Biden’s polling lead over Mr. Trump. Indeed, it has been almost 25 years since Bill Clinton sustained such a gaping advantage over his opponent, Bob Dole, in 1996.

But when donors and outside allies have been blunt with Mr. Trump and told him that he is, in fact, losing, the president has pushed back, claiming that things are getting better and there’s still plenty of time for improvement, according to Republicans familiar with these conversations who spoke on the condition of anonymity to disclose private exchanges.

“My polls show we’re getting real movement since Rushmore,” Mr. Trump has told multiple associates, referring to his Fourth of July address at Mount Rushmore, in which he framed the campaign as a battle against a “new far-left fascism” seeking to wipe out the nation’s values and history. White House advisers viewed the speech as a success, if a temporary one that was quickly overtaken by Mr. Trump’s defense of the Confederate flag. Yet the Biden campaign has not seen a real improvement in how voters view Mr. Trump since the beginning of the pandemic, according to a person who was familiar with the campaign’s data. Voters’ impressions of Mr. Trump, the person said, have only grown more negative.

In private conversations, Mr. Trump has also brought up the general election debates as an opportunity for him to improve his standing in the race, telling allies he expects his opponent to perform poorly in that format.

Mr. Trump’s view of his position in the race is partly belief in his own myth after the 2016 victory — the prognosticators were all wrong, and he was right — and partly the rosier-than-reality picture that he hears from certain advisers about the state of the race.

A president who loves numbers — the stock market when it’s on the rise, the monthly job report when it spells a positive story line for him — particularly loves polls, such as in the 2016 primary season, when he was outpolling his Republican rivals. He also has a great out if he doesn’t like the polls: November 2016.

His sources for his poll numbers, beyond cable television and newspaper articles, are his aides, some of whom willfully distort the electoral landscape to avoid his wrath — going so far as to tell him he’s winning in states like Maine, where he is losing. Aides said that even those advisers who are willing to bring him bad news no longer deliver the full picture.

One of Mr. Trump’s main pollsters, Tony Fabrizio, often had the most dire predictions and was known not to shy away from a “sky is falling” briefing with the president. But aides said that everyone has tiptoed around the president ever since June, when he threatened to sue Mr. Parscale after he presented polling data that showed Mr. Trump trailing Mr. Biden in several crucial states.

Now, aides said, even the aides with more dire predictions will explain away bad numbers by pointing to outside factors and will often blame news coverage for Mr. Trump’s slump.

The campaign disputed that there was anything terrible they even needed to brief the president about.

“We track 17 states that will decide who the next president will be and we trust the methodology,” said Tim Murtaugh, the campaign’s communications director. “In those states, our data shows that President Trump remains strong against a defined Joe Biden and is well positioned for re-election. ”