Could Trump really serve three terms? Don't bet against it ...

It is noon on 20 January 2029. In the biting cold of Washington, thousands of people are gathered on the National Mall to witness the swearing in of a new US president. Or, more accurately, an old US president: Donald Trump, aged 82, starting his third term in office.

- David Smith

For millions of Americans, this scenario may be the stuff of nightmares. But in Trump's mind, it is not far-fetched at all. Last weekend, he told an interviewer that he was "not joking" about another run and said there were "methods" to circumvent the constitutional limit of two terms for a president.

For longtime Trump watchers, it smacked of a familiar playbook used by the US right and the Maga movement: float a trial balloon, no matter how wacky or extreme; let far-right media figures such as Steve Bannon make the case that it is not so outlandish because, after all, Democrats are worse; stand by as Republicans in Congress avoid, equivocate, then endorse; and watch a fringe idea slowly but surely become normalised.

"One of the most important lessons of the last decade is the way that ideas have migrated from the fever swamp into the mainstream," said Charlie Sykes, a conservative author and broadcaster. "We've seen that migration of ideas that seem absurd but develop a constituency."

This one is a long shot. The constitution's 22nd amendment, ratified in 1951, states: "No person shall be elected to the office of the president more than twice." Legal experts and constitutional scholars reject any credible legal basis for a third term.