When Jamie Dimon surprised the political and financial elite early this year by praising some of Donald J. Trump’s policies, the longtime Democrat set off speculation that he had switched his allegiance to the Republican candidate.

He has done little since to tamp that down. The usually outspoken chief executive of JPMorgan, the nation’s largest bank, has been uncharacteristically vague about his political leanings of late. In an interview last week, he even left open the door to endorsing Mr. Trump — whose behavior in the aftermath of the last election Mr. Dimon once described as “treason.”

In private, however, Mr. Dimon has made clear that he supports Vice President Kamala Harris and would consider a role, perhaps Treasury secretary, in her administration. He has also told his associates that the former president’s 2020 election denialism remains close to a disqualifying factor. Those views were shared by three people who asked not to be identified discussing his politics because Mr. Dimon was speaking privately.

Mr. Dimon isn’t making his stance known publicly because he’s fearful that if Mr. Trump is victorious, he could retaliate against the people and companies who publicly opposed his run, his associates said. That’s a concern shared by other powerful corporate executives, and not without reason: Mr. Trump has begun to increase threats of political retribution in recent weeks.

Both the Trump and Harris campaigns have sought Mr. Dimon’s public support, and Mr. Trump once — falsely — declared that he had it. But for a man who has been eager to weigh in on virtually any topic — Ukraine, inequality, immigration — Mr. Dimon’s silence reflects a discomfort with the idea of staking out a public position on a contentious issue, people close to him say.

His quiet has been noticed in Washington and on Wall Street, where his every utterance is tracked. Fans, rivals and the odd detractor note with some alarm that Mr. Dimon, 68 years old and a billionaire, hasn’t made his specific stance on the election known.