Donald Trump stood before the United Nations on Tuesday and threatened to “annihilate” Iran. Yet even as the most powerful man on the planet flexed his military muscles, he was powerless to keep the gravitational pull of domestic politics at bay.

Heading into the UN building in New York, the US president was questioned by Kaitlan Collins, an anchor at CNN, which he had banned from the White House before a judge ruled against him. “I’m surprised that CNN is here covering me,” the 80-year-old snapped. “You should not be here covering me.”

The lashing-out was a reminder that even Trump, who has expanded executive power and dominated the national consciousness, finds some things beyond his control. Indeed, 20 months into his second term, there is a widening gap between the president’s self-perceived invincibility and the reality of his waning influence.

Federal courts are reining him in. Congressional Republicans are straying from the script. Poll numbers are tumbling to historic depths, driven by persistent inflation, rising fuel costs and an increasingly unpopular war in Iran. For the first time since his improbable political resurrection, Trump’s aura of authority is fading.

Rick Wilson, a longtime Republican strategist, prophesied: “This is the beginning of the end. This is the decline. As powerful and transgressive as he’s been, the country does not have a positive outlook right now. In fact, the negativity and pessimism among voters has reached a point that is unparalleled since Jimmy Carter.”

Trump’s self-belief never wavers. He faced four criminal cases and two assassination attempts before winning the 2024 election. He has lived by a mantra of “it will all work out well in the end” while his supporters wear hats that state: “Trump was right about everything.”

Yet he has had a rough month. The Federal Reserve defied him on interest rates. The supreme court blocked his administration’s attempt to impose new restrictions on mail-in ballots for November’s midterm elections. One judge prevented him adding his name to the Kennedy Center, prompting him to threaten the national arts complex with demolition; another judge blocked his ban on three news outlets from the White House grounds, ordering the administration to “immediately return, reinstate and restore” their access.

Now even Trump’s dependable power base, the Republican party, is showing cracks amid fears that he will cost them seats in November. In Florida, his home state, gubernatorial candidate Byron Donalds quietly scrubbed most Trump references from his campaign website, while the congresswoman María Elvira Salazar ran campaign advertisements openly declaring that federal immigration enforcement had gone “too far” and asserting that Latino voters “feel betrayed”.

Wilson, a co-founder of the Lincoln Project, an anti-Trump group, sees a herd mentality among congressional Republicans and compares the current mood to a wildlife documentary.

“It needs a David Attenborough voiceover,” he said. “It’s like the gazelles wandering the savannah. They’re sniffing the wind now and they smell something in the wind. They know it’s a predator but they don’t know what to do about it yet. What they haven’t realised is that the predator has been among them all along. The risk factor that they face now is Trump.”

For nearly a decade, elected Republicans maintained a posture of submission, fearful of drawing a primary challenger or a scathing post on Truth Social. But with the elections looming and control of Congress hanging in the balance, self-preservation is rapidly overriding loyalty to the president.

Wilson said: “Now it’s reached the point where the magic doesn’t work any more. There’s no political upside from a president who is at 29% approval rating in some polls, has presided over a disastrous war, and has ended up raising energy prices and food prices – all the things that they can’t spin away.

“The voters now have very much put that together. They associate the war with Trump. They associate the gas prices with Trump. They associate the grocery prices with Trump.”

This creates a vicious circle, Wilson argues. “The more he becomes a liability, the more he acts out. The more he demands loyalty from people and doesn’t get it, the more he demands loyalty from people and doesn’t get it. Everything was handed to him for a decade by that party and, now that they’re paying the price, they’ve decided this has got a little too hairy.”

Faced with shrinking authority and a hostile economic landscape, Trump has reverted to his trusted playbook: manufacturing spectacle, picking cultural fights and raging against the press. His recent decision to ban the news outlets CNN, MS Now and Politico from the White House campus following critical coverage was viewed by critics not as a display of strength, but a symptom of deep frustration.

The administration rejects such charges and insists that the president’s agenda is succeeding. Davis Ingle, a White House spokesperson, said in an email: “President Trump is the unequivocal leader, best messenger, and unmatched motivator for the Republican Party, and he is committed to maintaining Republican majorities in Congress.

“The president signed the largest working-class tax cuts in history, lowered the cost of prescription drugs, sealed the border, drove violent crime to the lowest level in nearly a century, unleashed an energy revolution, added more than a million private-sector jobs, and sent Americans’ 401(k)s climbing to record highs,” he added. “The choice has never been more clear: doubling down on President Trump’s winning, commonsense agenda or the Democrats’ extreme liberal policies and obstruction.”

But the trend lines are only set to worsen for Trump. If Democrats gain control of the House of Representatives next year, they plan to launch investigations into how he has allegedly abused his office to enrich his family, grant favours to supporters, hollow out the federal government and carry out expensive construction projects. The attention economy, meanwhile, will inexorably shift to the 2028 presidential race and the question of succession.

Bill Galston, a senior fellow at the Brookings Institution thinktank in Washington, said the inevitable shift of focus toward potential candidates – such as the vice-president, JD Vance, or the secretary of state, Marco Rubio – will be cause for friction.

“Nothing will drive him crazier than the shift of the spotlight away from him,” said Galston, a former domestic policy adviser to Bill Clinton. “The prospect of passing the torch, giving up the spotlight, is intensely painful for him. It’s his oxygen. Will he be able to breathe, spiritually and emotionally speaking, without it?”

Trump is not the first president to run into trouble after winning re-election. From Richard Nixon’s Watergate downfall to Clinton’s impeachment and George W Bush’s quagmire in Iraq, second terms have historically served as the graveyard of presidential ambition.

Allan Lichtman, author of a new book, Great American Presidents: The Twelve Who Transformed the Nation, calls it “the second term curse”. He noted: “Second terms have been remarkably difficult for presidents.”

Lichtman, a history professor at American University in Washington, believes that Trump is driven by two things: money and glory. “He cannot stand not being the centre of attention and that’s dangerous,” he said. “I don’t care much about his verbal lashing-out; I don’t think that helps him at all. But who knows what crazy things he might do to reassert attention on him? And that’s frightening.

“Never underestimate the power of the president. Just because Republicans are criticising him, his poll numbers are low, prospects for Republicans look dim, doesn’t mean he doesn’t have enormous power – and he is certainly quite willing to use that power unconstrained. He doesn’t care about the courts and doesn’t care about the Congress.”

From this perspective, Trump’s last refuge will be the unchecked use of executive authority, a politicised justice department and a sweeping pardon power. With nothing to lose in his final two years, he could go out all guns blazing.

Charlie Sykes, a conservative author and broadcaster, said: “Donald Trump fears irrelevance more than anything and he’ll rage against it as long as he can. The notion that he will go quietly would be incredibly naive.

“We’re headed for a collision between a lame duck who has no respect for the constitutional norms and an opposition that may have some power to hold him accountable. The paradox is the weaker he gets, the more dangerous he gets.”