There are few people who have believed in President Trump as firmly and unapologetically as Stephen K. Bannon, his former top White House adviser and top campaign strategist. And Bannon swore in a "60 Minutes” interview that aired Sunday that he would stand by Trump and fight, from the outside, against those he thinks are steering the president in a bad direction.

But even Bannon thinks Trump got something very important wrong. Very wrong. Quite possibly wronger than any president in decades.

In his interview with Charlie Rose, Bannon strongly suggested that Trump's firing of FBI Director James B. Comey was the biggest mistake in modern political history. And that's not even reading too much into Bannon's comments. He wasn't baited into it, either; he clearly signed off on that characterization.

Here's the exchange:

ROSE: Someone told me you described the firing of James Comey — you’re a student of history — as the biggest mistake in political history. BANNON: That’s probably too bombastic even for me, but maybe modern political history. ROSE: The firing of James Comey was the biggest mistake in modern political history? BANNON: If you’re saying that’s associated with me, then I’ll leave it at that.

Wow.

2. WATCH: Bannon says firing of Comey was the biggest mistake in modern political history. Also, he refuses to answer if Kushner was for it. pic.twitter.com/d0zcZgowd1 — Yashar Ali 🐘 (@yashar) September 11, 2017

Bannon has been willing to differ with Trump when Trump ran afoul of his nationalist ideals, to some degree. But there has been basically nobody more willing to sign off on Trump's most controversial tendencies. In the same interview, Bannon defended both Trump's response to recent violence in Charlottesville — which drew widespread GOP condemnation — and his hot-mic moment in that “Access Hollywood” tape talking about grabbing women by their ... well, you remember.

Bannon sees the best in Trump, and when Trump tilts in the wrong direction, Bannon often views it as someone else's fault — someone with undue influence on the president of the United States.

But even he sees the disaster that has emanated from the decision to fire the man who had been in charge of the Russia investigation. Even he recognizes the magnitude of the unforced error that was.

“I don’t think there’s any doubt that if James Comey had not been fired, then we would not have a special counsel, yes,” Bannon said, moments before the comments above. “We would not have the [special counsel Robert S.] Mueller investigation. We would not have the Mueller investigation in the breadth that clearly Mr. Mueller is going.”

To give you a sense of the mistakes Bannon apparently believes this surpassed in modern political history — and please understand that whatever you think of Bannon, as Rose noted, Bannon has studied history — he's suggesting that it was bigger than the Iraq War, the Vietnam War, the Affordable Care Act, Mitt Romney's "47 percent,” Hillary Clinton's “basket of deplorables,” Iran-contra, Richard Nixon's “Saturday Night Massacre,” etc.

Bannon admitted that saying it was the biggest political mistake ever would be “too bombastic” even for him. But he clearly doesn't think it's so outlandish to suggest that it was bigger than lots of things in recent decades. And as a top Trump ally — and someone privy to the inner workings of the White House for its first seven months — that's an astounding admission.

It also suggests that he knows this may not end well.

Further reading:

Steve Bannon’s nervous defense of Trump on Russia is telling

Steve Bannon is ‘a good Catholic,’ Charlie Rose said on ’60 minutes.’ Was he right?

Trump tortured Spicer and Priebus. Now they get to tell investigators about Trump.