Former Trump aide explains why president keeps people like Kellyanne Conway around -- even when she trashes him

Former White House aide Cliff Simis has a new book coming out that exposes Kellyanne Conway as a fraud. But worse, according to Sims, President Donald Trump is fully aware of it and wants to keep her anyway.

In a Monday interview with "Late Show" host Stephen Colbert, Sims recalled the story that he caught Conway blasting the White House staff while her iMessage on her iPhone while it was synced to her computer. Colbert asked how the president manages to keep people like that around when it's clear they hate him or don't think very highly of him.

"Why won't he fire her?" Colbert asked. "Why won't he trash her publicly? It makes no sense to me. He'll attack anyone. Why not her?"

"Well, one of the things I try to do int his book is help people understand what makes Donald Trump tick," Sims said. "And one of the things I think that is true about Kellyanne, and others, is 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. And he knows that she's a reliable -- you know, she will go out there on any show and defend him. And like I said, that never goes out of style."

Colbert asked for clarification, wanting to know if it was private loyalty that matters less to the president over public loyalty.

"I think that there's no doubt that public loyalty to the president is of the utmost importance to him," Sims said.

Conway's husband, George Conway has spent over a year trolling the president online, posing many to wonder how their marriage lasts when it seems they're so opposed to each other's ideology. Sims made it seem like they're a lot close than most might think.

Watch the interview below: