“As Trump’s stock rises in the Republican Party, so does Biden’s” with Democrats, said Brad Howard, a lobbyist and former aide to members of the moderate Blue Dog Coalition in the House. “If President Trump is still a factor, that is a continued benefit for President Biden and his case for renomination.”

The prospect of a “heavyweight fight” helps “both Biden and Trump,” added a prominent House progressive who spoke on the condition of anonymity to avoid upsetting liberals who aren’t thrilled with Biden. The Republican response to the FBI search of Trump’s Mar-a-Lago home “all but assures them both the nomination,” the lawmaker said.

The unprecedented investigation into a former president — one who is a likely candidate for his old job — creates a labyrinthine set of political risks and opportunities for Biden and Trump. For Trump, the greatest threat is becoming toxic to voters because of an indictment or conviction. Biden has to walk a tightrope between partisans who want him to ensure that Trump is prosecuted and voters who may see such a move as an abuse of power that unfairly targets a political adversary.

Biden appears to have chosen the cautious and traditional route of letting Justice Department officials speak — or act — for themselves. “It’s not even Biden’s style to use something the Justice Department does to his political advantage,” said a source close to the White House who spoke on the condition of anonymity.

By contrast, Trump frequently berated his attorneys general in public and urged them to pursue legal actions that aligned with his political interests. He blasted Attorney General Jeff Sessions for recusing himself from a probe of Trump’s ties to Russia and for failing to charge his 2016 rival, former Secretary of State Hillary Clinton, with crimes. In the waning weeks of his presidency, Trump pressured Justice Department officials to declare falsely that he was the victim of fraud when he lost the 2020 election to Biden, according to the testimony of several officials who appeared before the House committee investigating Trump’s role in the Jan. 6, 2021, attack on the U.S. Capitol.

The question of whether Biden would explicitly politicize legal action against Trump is different from the question of whether he would benefit from a federal case against Republicans’ leading 2024 hopeful. Just as Trump understood the potential damage that could be done by an investigation — the House impeached him for withholding security funds from Ukraine to try to force a probe of Biden in that country — Biden clearly grasps that even the appearance of political interference would rob him of a key contrast with Trump.

“No good comes in inserting yourself,” Jay Jacobs, chairman of the New York Democratic Party, said. “It only diminishes the credibility of the professional investigations that are going on.”

That’s a view shared by the White House.