The Supreme Court's decision not to rule quickly on whether Donald Trump can be prosecuted on election-subversion charges may help delay his trial, according to ex-prosecutors.

But they told the BBC this strategy of filing repeated challenges will only put off the inevitable and could even backfire on the former president in terms of timing for his White House campaign next year.

On Friday the justices declined to rule on whether Mr. Trump has immunity from prosecution in the case, turning down special counsel Jack Smith's request to take up the matter in an expedited manner.

The Supreme Court offered no explanation, saying only that Mr. Smith's petition “was denied”.

The special counsel's office has not yet commented on the decision, which is seen as a major setback to his case against Mr. Trump.

It is unclear, however, how long the trial might be delayed, or whether it might be pushed back beyond the 2024 election.

Mr. Trump is currently the Republican frontrunner for a rematch against President Joe Biden next November.

The special counsel indicted the ex-president in August for allegedly conspiring to overturn the results of the last election in the lead-up to the US Capitol riot on 6 January 2021.

Friday's ruling means that the US Court of Appeals for the DC Circuit will have to hear the case first. But eventually, it is likely the Supreme Court will have to make a ruling anyway.

Mr. Smith had argued that the appeals process could delay the start of the trial, which is due to begin on 4 March.

For now, the judge in the case, Tanya Chutkan, has paused proceedings while Mr. Trump's legal team appeals. He has repeatedly argued he has immunity from prosecution because he was acting in an official capacity at the time of the riot.

Gene Rossi, a former federal prosecutor with decades of experience at the US justice department, told the BBC the decision is a “huge setback for Jack Smith on the scheduling front".

“However, his request for expedited review was a noble attempt to move this trial along,” he added. “Mr. Trump, whose immunity appeal is not strong, will not face the 6 January music for multiple months.”

Mr. Rossi added that Judge Chutkan “does not care one iota that he is a presidential candidate” and, despite the appeals process, will still want her trial to move “with utmost alacrity”.

The trial, he added, may ultimately end up being pushed back to late July or early August - which would fall shortly after the Republican National Convention, beginning on 15 July.

“Simply put, that would be a scheduling hot mess,” he said. “The worst thing [for Mr. Trump] would be to have a jury considering whether he's basically an insurrectionist at that time. That's not good for your campaign... he's delaying the inevitable.”

Another former federal prosecutor, Case Western Reserve University Professor Kevin McMunigal, said that the Supreme Court's decision "is not surprising", given that a "typical pattern” in a legal case would be for an appeals court to decide on a matter before it is brought to the high court.

“But I'm not sure that this will necessarily delay the trial," he added.

Gregory Wallance, a former federal prosecutor who helped convict seven lawmakers for bribery as part of an FBI sting in the late 1970s, told the BBC: “It's a win for Trump.

“But how big a win depends on whether his appeal of the immunity ruling delays his January 6 trial until past the election, which right now is unpredictable.”

A fast-tracked process would not have been without precedent.

Carl Tobias, a law professor at the University of Richmond in Virginia, told the BBC that the Supreme Court expedited 19 cases in the last four years.

In 1974 the justices fast-tracked the case of US v Nixon, which led to the release of the Watergate tapes, dealing a fatal blow to the presidency of Richard Nixon.

“Trump's delay strategy appears to be working,” Mr. Tobias said.

“All of [this] will consume time, and, thus, complicate efforts to start the trial before Judge Chutkan on the early March date.”

Arguments are set to be heard in the case in DC Circuit Court on 9 January.

It is one of two election-subversion indictments against Mr Trump. He also faces two other criminal cases, one over classified papers and another to do with hush money. (BBC)

•Donald Trump was indicted on election subversion charges in a Washington DC court on 1 August.

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