If you think you've seen this movie before, it's because you have -- except the second time will be even more nerve-racking. Yes, world: get ready for Biden vs Trump 2.

That's a potential takeaway from the scandal embroiling Donald Trump over his alleged hoarding of secret government documents almost two years after losing reelection to Joe Biden.

If Trump was previously considered likely to announce a 2024 comeback bid, one school of thought is that the FBI search of his Florida estate, allowing Trump to depict himself as a martyr, makes that decision almost certain.

"I believed he was gonna run before -- I'm stronger in my belief now," Republican Senator Lindsey Graham told Fox News.

If Trump does run, goes the theory, then Biden surely does, too. Despite being the oldest man ever in the job at 79, Biden sees it as his historic mission to rid the United States of Trump.

And so, after surviving the tense, at times nightmarish 2020 election, Americans may do it all over again.

This time it would be in reverse -- the incumbent a by-then 81-year-old Biden and the challenger a 78-year-old Trump.

Given Trump's constant lies that he won the 2020 election and searing evidence of his role in stoking the violent January 6 assault on Congress, a rematch would be ugly.

"If you think Trump's 2016 and 2020 campaigns were nasty, you ain't seen nothing," said American University history professor Allan Lichtman, a leading authority on US presidential elections.

To practitioners of the dark political arts, the FBI raid on Trump's Mar-a-Lago resort is a game-changing moment that, ironically, could benefit either side.

For Biden the logic is obvious.

The biggest name in the Republican Party is on the ropes, facing not only the FBI probe, but legal cases linked to allegations of everything from subverting the election, to fraud and rape.

That's embarrassing for Republicans and energizing for Biden's Democrats, who increasingly dream of avoiding a predicted wipe-out, or even scoring their own surprise victory, in November midterm elections to decide control of Congress.

"Trump is like a steroid boost for Democrats," Jim Kessler, at the Democratic think tank Third Way, told The Hill.

As the Republican-supporting Wall Street Journal editorial board says: Republicans "should be making the midterms a referendum on Mr Biden's first two years. Democrats would prefer to talk until November -- really, until the end of time -- about Mr Trump."

Yet Trump will also see benefits.

Once again he's dominating the national psyche, while his fervent base has a new conspiracy theory to feed off, lighting up right-wing social media with calls to arms and threats of Civil War 2.0.

"Donald Trump has more than $100 million in his political war chest. But he has something even more valuable -- an active FBI investigation against him," wrote Richard Lowry, editor of the conservative magazine National Review.

"It has put him front-and-center again. It has made it easy for him to portray himself as an embattled victim."

In a Republican primary, Trump's political footprint would likely crush the strongest of rivals.

"If Trump wants it at this point, I don't see how it's not his," Republican political strategist John Thomas told Politico. "It'll be a coronation."

And Trump getting in would also essentially trigger Biden's decision to follow -- scotching any thoughts he may privately have of stepping aside for a younger figure before 2024.

"Trump is the critical first mover in whether or not there is a rematch," said Lara Brown, director of the Graduate School of Political Management at George Washington University.

"I do believe that President Biden is waiting to see if Trump declares and if he does, I believe he will also declare very quickly after."

Voters may not want either man.

A July poll by NewsNation/Decision Desk HQ found 60 percent said Biden shouldn't run in 2024 and 57 percent said the same of Trump.

Biden backs himself against Trump. "In the next election, I'd be very fortunate if I had that same man running against me," Biden said in March.

While it's been a difficult year for Biden, the last couple months have seen him turn his presidency around, racking up remarkable legislative and policy successes.

And although Biden remains deeply unpopular, with approval ratings around 40 percent, the improved record in the White House, and widespread anger at the Supreme Court's overturning of national abortion rights, leave advisors optimistic.

So while Republicans get lost in Trump dramas, Democrats will focus on kitchen table issues, an aide said.

"This is about meeting people where they live and the things that matter most in their lives," the aide said, speaking on condition of anonymity. "There'll be a lot of things that will be in the news, but we are going to speak to people in their lives."