Top Trump administration officials are investigating an Instagram post made by a former FBI director, James Comey, that depicted “8647” spelled out in seashells, an image that Mr. Comey’s detractors say is a call to have President Trump “assassinated.”

“Cool shell formation on my beach,” Mr. Comey wrote in a caption in the Instagram post, which has since been taken down. In a follow-up post, Mr. Comey pleaded ignorance of the use of “86.”

“I didn’t realize some folks associate those numbers with violence. It never occurred to me but I oppose violence of any kind so I took the post down,” Mr. Comey wrote.

But the full force of the Trump administration is now focused on Mr. Comey. The FBI director, Kash Patel, said on X that his agency is in contact with the Secret Service — which investigates threats against the president — “and will provide all necessary support.”

The homeland security secretary, Kristi Noem, who oversees the Secret Service,  said on X: “Disgraced former FBI Director James Comey just called for the assassination of  @POTUS  Trump.  DHS and Secret Service are investigating this threat and will respond appropriately.” 

On Fox News Thursday night, the director of national intelligence, Tulsi Gabbard, said Mr. Comey “should be held accountable and put behind bars for this.”

The shell formation, which Mr. Comey claims he “saw” on his beach (thereby claiming that he did not make the shell formation himself), is a reference to “86-ing” Mr. Trump, who was represented by the number 47, for 47th president. 

The term “86” has several connotations, from refusing a drunk customer service to the standard 86-inch depth of a grave in the United States. 

“In the days before a safety fence was installed on the observation deck of the Empire State Building, people would commit suicide by jumping from it. The deck was on the 86th floor,” George Mahe wrote years ago in St. Louis Magazine.

A former FBI agent was left in disbelief that Mr. Comey, once the most powerful law enforcement official in the country, would play dumb over the meaning of “86.”

“James Comey is the worst kind of narcissist and continues to bring shame and discredit upon the FBI he once proclaimed to revere,” a retired FBI agent, James A. Gagliano, told the Sun.

“To pretend not to know what ‘86’ means in street slang, and then cop out in his apologia by claiming he thought it was ‘political’ — but not a call for violence — turns my stomach,” Mr. Gagliano added.

Mr. Trump appears to despise Mr. Comey, going back to his first administration. Mr. Comey was the FBI director when Mr. Trump came to office, and the two men immediately clashed over the Russia investigation. After Mr. Trump had Mr. Comey fired in 2017, Mr. Comey then emerged as a standard-bearer of the resistance to the Trump administration.

Mr. Comey’s social media gaffe comes at the same time his daughter, Maurene Ryan Comey, is an assistant U.S. attorney — in the same office, the Southern District, that her father once led — serving as the lead prosecutor in the sex-trafficking trial of Sean “Diddy” Combs. 

In a statement, the Secret Service said it “vigorously investigates anything that can be taken as a potential threat against our protectees” and was aware of “the social media posts in question.”