Former Secretary of State John KerryJohn Forbes KerryRubio wants DOJ to find out if Kerry broke law by meeting with Iranians Time for sunshine on Trump-Russia investigation Pompeo doubles down on criticism of Kerry: The Iran deal failed, 'let it go' MORE said the anonymous op-ed published in The New York Times, purportedly written by a senior administration official who's part of an internal "resistance" against President TrumpDonald John TrumpLondon terror suspect’s children told authorities he complained about Trump: inquiry The Memo: Tide turns on Kavanaugh Trump to nominate retiring lawmaker as head of trade agency MORE, shows that Trump is incapable of the basic duties of the office.

In an interview on "The Late Show with Stephen Colbert," Kerry said Trump is "not capable of doing the job or living up to the responsibilities."

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"It scared the hell out of me," he said, referring to the op-ed. "You know what it really means, Stephen, is that we don't really have a president."

"[But] there is a reassurance," Kerry added. "It means that James Buchanan is no longer our worst president."

His remarks came in response to the Times op-ed published on Wednesday that referenced coordinated efforts by some administration officials to “thwart” Trump’s “worst inclinations.”

Kerry also talked about an anecdote in veteran journalist Bob Woodward's upcoming book that paints a picture of dysfunction at the White House.

"I mean you've got somebody stealing something off of the president's desk in order to prevent him from making a decision," Kerry said, referring to a report that now-former National Economic Council Director Gary CohnGary David CohnPoll: Majority believes Woodward book and NY Times op-ed about Trump admin Cohn: Jamie Dimon would be 'phenomenal' president On The Money: Trump announces new China tariffs | Wall Street salaries hit highest level since 2008 | GOP bets the House on the economy MORE removed a document from Trump's desk regarding plans for the U.S. to withdraw from the North American Free Trade Agreement.

"You have him ordering generals to do something, and within a minute of them being ordered they turn to their fellow generals and say, 'We're not doing that,'" he added.

Kerry, a former senator who was the Democratic presidential nominee in 2004, is thought to be considering a possible reentry into politics. He has refused to say whether he has ruled out a bid to challenge Trump in 2020.

“Talking about 2020 right now is a total distraction and waste of time,” Kerry told CBS News last month. “What we need to do is focus on 2018. We need to win back the confidence of the country to move in a better direction and to do it in sensible ways."