President Donald Trump won’t likely fire or publicly trash White House counselor Kellyanne Conway for one big reason, according to one of the president’s former aides.

Cliff Sims — whose tell-all book Team of Vipers, about his 500 days working as Trump’s director of message strategy, was published Tuesday — told “The Late Show” host Stephen Colbert on Monday that Conway’s standing was all about loyalty.

“One thing that never goes out of style in the Trump White House is someone who’s willing to go out on TV and just fight it out with somebody,” Sims explained. Trump, according to Sims, knew Conway was willing to “go out there on any show and defend him.”

That was even amid rumors that Conway had been criticizing Trump in private, and her attorney husband George Conway’s very public criticism of the president on Twitter.

Colbert asked if public loyalty was more important to Trump than private loyalty.

“I think that there’s no doubt that public loyalty to the president is of utmost importance to him,” Sims replied.

Check out the clip here: