Miles Taylor, a former chief of staff at the Department of Homeland Security, has published an essay on the online platform Medium explaining his decision to write the 2018 essay and a subsequent book entitled A Warning.

"I saw Donald Trump prove he is a man without character and his personal defects have resulted in leadership failures so significant that they can be measured in lost American lives," Taylor wrote.

"So when I left the administration I wrote A Warning, a character study of the current commander in chief and a caution to voters that it wasn't as bad as it looked inside the Trump administration - it was worse," Taylor continued.

In the anonymous essay, which drew widespread attention after claiming its author was a senior administration official, Taylor said some political appointees were actively working to undermine the president's worst impulses.

The essay riled Trump, who ordered his team to begin looking for leakers in the White House.

Taylor served in DHS from 2017-2019, including as chief of staff for former DHS Secretary Kirstjen Nielsen, who was widely criticised for overseeing a policy at the US southern border that saw immigrant children separated from their parents.

He has been openly critical of the Trump administration while working as a contributor for CNN in the lead up to the November US presidential election.

Australian Associated Press