New York Magazine contributing editor Gabriel Sherman on Tuesday reported on a remarkable conversation he had with a senior Republican official, who described imagined conversations Donald Trump’s chief of staff Gen. John Kelly and defense secretary James Mattis have had about “physically [restraining] the president” in the event he “[lunges] for the nuclear football.”

Sherman was discussing the growing concern in the West Wing over Trump’s temperament, particularly as the president continues to escalate feuds with prominent Republicans like Secretary of State Rex Tillerson and Sen. Bob Corker (R-TN) while simultaneously setting the United States “on the path to World War III.”

“A conversation I had with a very prominent Republican today, who literally was saying that they imagine Gen. Kelly and Secretary Mattis have had conversations that if Trump lunged for the nuclear football, what would they do?” Sherman told NBC’s Chris Hayes. “Would they tackle him? I mean literally, physically restrain him from putting the country at perilous risk.”

“That is the kind of situation we’re in,” Sherman added.

Pressed by Hayes to explain the sources’ relationship to—and direct knowledge of—the Trump administration, Sherman explained, “these are the conversation they have, on very good authority, are taking place inside the White House.”