Republican Donald Trump is suggesting that rival Hillary Clinton’s emails may be responsible for the death of an Iranian nuclear scientist who was executed for spying for the United States.

“Many people are saying that the Iranians killed the scientist who helped the U.S. because of Hillary Clinton’s hacked emails.”

Tweeted back Clinton spokesman Nick Merrill-

“’Many people are saying’=’I made this up.’”

Mr. Merrill added that after Mr. Trump’s morning speech to the Detroit Economic Club and sticking closely to his script “the muzzle was bound to come off.”

Mr. Trump’s speech was designed in part to reassure Republicans unnerved by a disastrous week of self-inflicted feuds with an assortment of people, from grieving Muslim American parents to the leaders of Mr. Trump’s own party. Clinton’s campaign cast his tweet on Monday night as evidence that, in the words of spokesman Josh Schwerin, “There’s just no resetting Donald Trump.”

Mr. Trump isn’t the first to suggest there could be a link between Ms. Clinton’s emails on her private server and the execution of Shahram Amiri.

Arkansas Republican Sen. Tom Cotton said on CBS’s “Face the Nation” Sunday that there “were on Hillary Clinton’s private server, there were conversations among her senior advisers about this gentleman.”

“That goes to show just how reckless and careless her decision was to put that kind of highly classified information on a private server,” he said.

Amiri, an Iranian scientist, defected to the U.S. at the height of Western efforts to thwart Iran’s nuclear program. When he returned to Iran in 2010, he was given a hero’s welcome and greeted with flowers by government leaders. Then he mysteriously disappeared.

Amiri’s case indirectly found its way into the spotlight last year with the release of State Department emails sent and received by Ms. Clinton. U.S. officials already had discussed his case publicly in 2010, including a $5 million payment offered to him if he stayed in the U.S. The State Department emails released to the public are mostly noteworthy because they provide an insider account of deliberations at the time.

One email forwarded to Ms. Clinton by senior adviser Jake Sullivan on July 5, 2010 just 10 days before Amiri returned to Tehran appears to reference the scientist.

“We have a diplomatic, ‘psychological’ issue, not a legal one. Our friend has to be given a way out,” the email by Richard Morningstar, a former State Department special envoy for Eurasian energy, read. “Our person won’t be able to do anything anyway. If he has to leave, so be it.”

Another email, sent by Mr. Sullivan on July 12, 2010, appears to obliquely refer to the scientist just hours before his appearance at the Iranian-interests section at the Pakistani Embassy in Washington became widely known.

“The gentleman … has apparently gone to his country’s interests section because he is unhappy with how much time it has taken to facilitate his departure,” Mr. Sullivan wrote.

Ms. Clinton’s decision to store her emails on a private server in her New York home sparked an FBI investigation and has become a dominant issue in the presidential campaign.