Trump continued: "His incredible wife, Karen, who I have a lot of respect for, once pulled me aside & said strongly that ‘John respects you greatly. When we are no longer here, he will only speak well of you.’ Wrong!”

According to The Atlantic , during a 75-minute speech and question-and-answer session at Drew University in New Jersey, Kelly defended Lt. Col. Alexander Vindman, whom Trump removed from the White House last week following Vindman’s cooperation with impeachment investigators. He also touched on North Korean leader Kim Jong Un, Russian President Vladimir Putin and Trump’s rhetoric on immigration.

Kelly was Trump's longest-serving chief of staff, holding the job for 18 months until leaving as Trump's top aide in December 2018. Prior to that, he'd served as Trump's first Homeland Security secretary, and ran U.S. Southern Command, which oversees military operations in Central and South America as well as the Caribbean. His scolding Wednesday is the sharpest criticism of Trump since he left the White House, though he has previously not hesitated to break with Trump since leaving government.

Two weeks ago, he said, “I believe John Bolton,” the former national security adviser who claimed in excerpts of a forthcoming memoir that Trump pursued a quid pro quo with Ukraine, according to news accounts of the book.

Before that, Kelly told The Washington Examiner he'd warned Trump not to replace him with a chief of staff who would be a "yes man," predicting that doing so would result in his impeachment — an assertion Trump reportedly denied.

He also countered Trump during last year’s historically long partial government shutdown, picking a fight with the president over his proposed border wall with Mexico.

Kelly is far from the only former White House official who’s crossed the president after leaving the administration. Trump has also lambasted Bolton, former Secretary of State Rex Tillerson, former Defense Secretary Jim Mattis and former aides Omarosa Manigault and Anthony Scaramucci after they each either implicitly or explicitly criticized Trump.

Bolton had Kelly‘s back, speaking up later Thursday to defend his former colleague, whom he called “an honorable man,“ against Trump‘s attacks while urging Republicans not to fall in line with Trump‘s broadsides.

“John and I have disagreed at times, as is commonplace at senior government levels, but he has always served his country faithfully,“ Bolton tweeted. “Conservatives especially have a responsibility to reject baseless attacks upon him.“