Four indictments of Donald Trump have set the stage for a surreal and potentially explosive US presidential election, with the presumptive Republican nominee on trial for seeking to overthrow the very democratic process he hopes will restore him to the White House.

The 77-year-old former Republican president will likely have to juggle campaign events with court appearances as he seeks to win the party's nomination next year and another term in the Oval Office.

Trump alleges that the barrage of federal and state charges filed against him in recent months is a plot by Democratic President Joe Biden -- his likely 2024 opponent -- to hamstring his White House bid.

"How can my corrupt political opponent crooked Joe Biden put me on trial during an election campaign that I'm winning by a lot?" the billionaire real estate tycoon said at a campaign rally in New Hampshire.

Trump said he was being forced to "spend time and money away from the campaign trail in order to fight bogus made-up accusations and charges."

While complaining about his legal woes, Trump has sought at the same time to turn them to his advantage, appealing for donations and claiming that they have only increased his popularity.

"Any time they file an indictment, we go way up in the polls," he said.

This does appear to be generally the case -- at least among the Republican rank-and-file who make up Trump's loyal base of supporters.

Jordan Tama, an associate professor at American University, said the upcoming criminal trials facing the former president are "certainly going to complicate Trump's campaign.

"He may need to leave the campaign trail at times to participate in the legal processes," Tama said, and divert some of his campaign cash to his burgeoning legal fees.

"But it's not really clear that having to participate in these trials is going to alter the contours of the election from a broad political standpoint," he said. The standing of the key candidates has remained largely unchanged, he added.

- 'Baggage' -

Trump has been charged by special counsel Jack Smith with conspiring to overturn the results of the 2020 election he lost to Biden and with retaining top secret government documents after he left office and thwarting investigators trying to recover them.

Smith has asked the judge who will preside over the conspiracy case to set a January 2024 date for the start of the trial, just days before the first Republican primary nominating contests in Iowa and New Hampshire.

The documents case is scheduled to go to trial in May 2024. Trump also faces election-related racketeering charges in Georgia and a trial in March in New York for allegedly paying hush money to a porn star.

Trump's rivals for the Republican nomination have tiptoed around his worsening legal woes while he continues to enjoy the support of the party faithful.

"The consensus is that at some point Republicans will catch on to the fact that Trump's baggage is getting heavier and heavier and losing to the Democrats is a greater probability," said Larry Sabato, who heads the University of Virginia's Center for Politics.

"Except that everyone's been predicting this consistently and it hasn't happened yet."

Tama said most American voters already have a fixed opinion about Trump.

"The voters who have supported him -- they're going to support him regardless of what's going on in the trials," he said. "The voters who don't like Trump are going to continue to not like him and be unwilling to vote for him."

He said if Trump wins the Republican nomination, the presidential election could come down to a small number of swing voters, some five to 10 percent of the population.

"I think for those voters, the legal processes will hurt Trump, because they're a reminder of the deep flaws that Trump has as a person and as a leader," he said.

"But it's not at all clear that this is going to determine the outcome," he said. "It seems likely that the election will hinge just as much on other things like the state of the economy that often influence the outcome of elections."