Vice-president Mike Pence says he is “100% confident” that none of his staff were behind an anonymous article that described Donald Trump as “amoral” and “erratic”.
He has offered to take a lie detector test “in a heartbeat” to prove he is not the author.
The article – apparently written by a senior Trump official – said “a quiet resistance” within the administration was working to thwart some of the president’s “worst inclinations”.
Speaking on CBS’s Face The Nation, Mr Pence said he had not asked his staff whether they were involved.
“I know them,” he explained. “I know their character.”
His aides are as keen as he is to advance Mr Trump’s agenda, he told the programme.
It has been suggested by Republican senator Rand Paul that the president would be justified in using lie detectors to find the article’s writer.
Mr Trump has not commented on whether he would go that far, but Mr Pence said he would not refuse.
“I would agree to take it in a heartbeat and would submit to any review the administration wanted to do,” he told Fox News Sunday.
Mr Pence said he did not know who had written the article, and whoever it was should resign.
The piece, in the New York Times, said that Mr Trump’s “erratic behaviour would be more concerning if it weren’t for unsung heroes in and around the White House”.
It added: “It may be cold comfort in this chaotic era, but Americans should know that there are adults in the room.
“We fully recognise what is happening. And we are trying to do what’s right even when Donald Trump won’t.”
The president has condemned the paper for publishing the article, saying: “They don’t like Donald Trump and I don’t like them.”
He described the anonymous writer as “gutless”, adding: “The Times must, for National Security purposes, turn him/her over to government at once!”