An anonymous Trump administration official who wrote a 2018 New York Times opinion article criticising the president has identified himself.
Miles Taylor is a former chief of staff at the Department of Homeland Security.
"We do not owe the President our silence," Mr Taylor said. "We owe him and the American people the truth."
When the column was published it sparked outrage in the White House, and set off a frantic investigation to try and find the author.
At the time, Mr Trump urged the justice department to investigate and also called the anonymous author "gutless".
Shortly afterwards, Mr Taylor wrote a book about working under President Trump, called The Warning. Its author was labelled as "Anonymous - a senior Trump administration official".
In a statement published on Wednesday, Mr Taylor, now a CNN contributor, said: "Much has been made of the fact that these writings were published anonymously. The decision wasn't easy, I wrestled with it, and I understand why some people consider it questionable to levy such serious charges against a sitting President under the cover of anonymity.
"But my reasoning was straightforward, and I stand by it. Issuing my critiques without attribution forced the President to answer them directly on their merits or not at all, rather than creating distractions through petty insults and name-calling. I wanted the attention to be on the arguments themselves."
Responding to Mr Taylor's statement, White House press secretary Kayleigh McEnany called him a "low-level, disgruntled former staffer".
White House Chief of Staff Mark Meadows called the revelation "a monumental embarrassment", adding: "I've seen more exciting reveals in Scooby-Doo episodes."
And at a rally in Arizona, President Trump said: "This guy is a low-level lowlife that I don't know."
But Mr Taylor attended many meetings with the president in his role at the Department of Homeland Security, the Associated Press reports.
In the initial 2018 article Mr Taylor said he was part of a secret "resistance" force that was working to undermine the president.
"Many Trump appointees have vowed to do what we can to preserve our democratic institutions while thwarting Mr Trump's more misguided impulses until he is out of office," he wrote.
The New York Times defended the editorial in a statement at the time, saying: "We are incredibly proud to have published this piece, which adds significant value to the public's understanding of what is going on in the Trump administration."
The identity of the author was hotly speculated on in Washington and in the media, with Vice-President Mike Pence and then UN Ambassador Nikki Haley among names discussed.