Former White House chief strategist Steve Bannon speaks to Charlie Rose on 60 Minutes. CBS News

President Trump's chief strategist Steve Bannon left the White House on August 18 after a turbulent tenure of shaping the president's first seven months in office. In his first television interview, Bannon speaks with Charlie Rose this week about those first months of the Trump administration — including what, he says, might be the biggest mistake in modern political history.

While Bannon wouldn't admit outright that he disagreed with the president when it came to firing F.B.I Director James Comey in July, he did acknowledge that it was a big mistake.

In the interview, Rose tells Bannon that he heard him describe the firing as the "biggest mistake in political history."

"That probably would be too bombastic, even for me," Bannon responds, "but maybe modern political history."

The way Bannon sees it, he tells Rose, the FBI is an institution, and swapping out the head of that institution wouldn't change its approach to the Russian investigation. Moreover, Bannon acknowledges that, had Comey still been at the helm of the FBI, special prosecutor Robert Mueller would have never been put in charge of the investigation.

"I don't think there's any doubt that if James Comey had not been fired, we would not have a special counsel," Bannon says.

During Bannon's time in the Trump administration, he and the president embraced the nationalist philosophy they both shared. Hillary Clinton overlooked populism at her peril, Bannon says.

"Hillary Clinton's not very bright," he tells Rose. "Everybody says she's so smart, so much smarter than Donald Trump."

"She doesn't really have a grasp. She doesn't have a grasp on what's important and what's not."

So, when Clinton attacked Breitbart News — Bannon's workplace before and after his time in the administration — as supporting white supremacists, she was missing the point, Bannon says.

"First off, not only is it morally wrong, it's also totally irrelevant," he says.

What Bannon feels is relevant is "economic nationalism" wherein American citizens are prioritized above everyone else.

"The only question before us: Is it going to be a left-wing populism or a right-wing populism," Bannon says. "And that is the question that will be answered in 2020."

Because Bannon thinks a faction of Democrats agree with his notion of populism, he thinks the Democratic Party needs a reckoning of its own.

"Here's the problem of the Democratic Party…" he tells Rose. "There's no Breitbart. The problem in the Democratic Party? They haven't had a civil war."

Until the Democratic Party comes to terms with its own discord, Bannon says, "they'll never be competitive."

"They have the same problem with their establishment we have with ours."

Why is President Trump's approval rating so low? Rose asked Bannon.

"I think he's 36% or 38% because we haven't gotten the wall built," Bannon says, explaining that once President Trump is able to enact his legislative agenda, he'll be closer to 47% approval.

Bannon goes on to predict that Republicans will pick up "six or seven Senate seats" in the 2018 midterms, and by 2020, President Trump will win in a landslide.

When it comes to the recent saber rattling with North Korea, Bannon tells Rose that the solution to preventing nuclear war is through China.

"My suggestion and my recommendation is to solve the problem in Korea, you need to solve that problem with China," he says. "It's a client state of China."

Bannon says to solve its China problem, the U.S. should utilize the "tremendous leverage" it has, including sanctions, capital markets, and Chinese banks and financial institutions.

Why hasn't the U.S. used this leverage to this point?

"You don't use this lightly," Bannon says. "It would have, by the way, it would have an impact here in the United States. There's no doubt about it."

Now out of the Trump administration, Bannon has returned to his former position as executive chairman of Breitbart News. During his interview at Bannon's Washington D.C. home — which doubles as the Breitbart headquarters —Rose also spoke to the conservative news organization's editor in chief, Alex Marlow.

"We have the opinion that news is the single most influential driver of the culture that there is right now, as Hollywood sometimes is at times," Marlow tells Rose in the clip above. "But right now, the news cycle is really driving the culture in a remarkable way."

Marlow tells Rose that the influence of Breitbart comes from "custom choosing" stories that they feel will resonate with their audience.

"We admit that we have a worldview, which is populist, nationalist, grassroots conservative," Marlow says. "We think CNN has just as powerful of a worldview as we do, as does the New York Times. They just won't admit it."