He took a step even Richard M. Nixon avoided in his most desperate days: openly ordering direct, immediate government action against specific opponents, timed to serve his re-election campaign.

“There is essentially no precedent,” said Jack Goldsmith, who led the Justice Department’s Office of Legal Counsel under President George W. Bush and has written extensively on presidential powers. “We have a norm that developed after Watergate that presidents don’t talk about ongoing investigations, much less interfere with them.”

“It is crazy and it is unprecedented,” said Mr. Goldsmith, now a professor at Harvard Law School, “but it’s no different from what he has been saying since the beginning of his presidency. The only thing new is that he has moved from talking about it to seeming to order it.”…

“I have worked for nine secretaries of state,” Mr. Burns said. “I cannot imagine any of them intervening in an election as blatantly as what we are seeing now. Our tradition is that secretaries of state stay out of elections. If they wanted to release Hillary Clinton’s emails, they could have done it in 2017, 2018 or 2019. It is an abuse of power by Donald Trump and Mike Pompeo.”