The Supreme Court that former President Donald J. Trump helped to shape tossed him a legal lifeline on Wednesday night, making a choice that substantially aided his efforts to delay his federal trial on charges of plotting to overturn the 2020 election.

By deciding to take up Mr. Trump’s claim that presidents enjoy almost total immunity from prosecution for any official action while in office — a legal theory rejected by two lower courts and one that few experts think has any basis in the Constitution — the justices bought the former president at least several months before a trial on the election interference charges can start.

It is not out of the question that Mr. Trump could still face a jury in the case, in Federal District Court in Washington, before Election Day. At this point, the legal calendar suggests that if the justices issue a ruling by the end of the Supreme Court’s term in June and find that Mr. Trump is not immune from prosecution, the trial could still start by late September or October.

But with each delay, the odds increase that voters will not get a chance to hear the evidence that Mr. Trump sought to subvert the last election before they decide whether to back him in the current one.

If Mr. Trump is successful in delaying the trial until after Election Day and he wins, he could use the powers of his office to seek to dismiss the election interference indictment altogether. Moreover, Justice Department policy precludes prosecuting a sitting president, meaning that, once sworn in, he could likely have any federal trial he is facing postponed until after he left office.

On its surface, the Supreme Court’s ruling on Wednesday night was a purely logistical decision. The justices decided to keep preparations for the trial on hold while they review a lower court’s rejection of the immunity defense. They set a hearing on the issue for the end of April.