Megyn Kelly got Charles Krauthammer's take on the latest developments surrounding Donald Trump's presidential campaign.

Trump has gone after Jeb Bush throughout his campaign, but has been mostly silent when it comes to his chief rival in the latest polls: Dr. Ben Carson. 

A new Monmouth University national poll put Carson way ahead of Trump (55-36%) in a hypothetical head-to-head matchup. The two were tied in a Monmouth poll this week in Iowa.

Calling Carson a "friend," Trump questioned what kind of job the neurosurgeon would do in the Oval Office when it comes to the economy. 

“He's really a friend of mine, I just think it's a very difficult situation that he puts himself into, to have a doctor who wasn't creating jobs and would have a nurse or maybe two nurses. It's such a different world. I've created tens of thousands of jobs over the years," Trump told The Daily Caller in an interview.

Krauthammer said he thought it was "impossible" to disparage Carson, but said Trump is saving the "heavy artillery" criticism for Bush. 

He said he believes Trump sees Bush as the biggest "establishment" competitor in the race, and that Bush has the financial backing to stay in the race until the end.

On Trump's loyalty pledge to the Republican Party, Krauthammer said he doesn't think it means very much. 

He said if Trump decides he hasn't been treated fairly by the GOP and loses the nomination, he could still launch a third-party bid. 

But Krauthammer said the document proves Trump believes he has a "good shot" to win the nomination, and that ultimately a third-party run will be unattractive to Trump because of the expense and the slim chance of victory.

"He's not gonna win and he doesn't like to end up losing. So I don't think it's an attractive alternative," he said.

Watch the full segment above to hear Charles' opinion on the ongoing Trump-Jeb feud. 

Tonight at 9p/12a ET, don't miss a powerful "Kelly File" special on the Black Lives Matter protests, with audience reaction. Megyn will look at whether the group is taking a dangerous stance and its impact on the 2016 race.