'BlacKkKlansman' director and stars on the Ku Klux Klan and the real-life inspiration behind the film

"BlacKkKlansman” is based on the true story of a black cop and the KKK in 1978.

In the midst of a time when Americans are grappling with issues of race and rage, anger and fear, a new film offers comic relief -- with the sharpest of edges.

Director Spike Lee’s newest movie "BlacKkKlansman" is based on the true story of a black cop in Colorado Springs who infiltrated the Ku Klux Klan in 1978. At one point, the film depicts the cop buddying up to an unsuspecting David Duke, then the KKK grand wizard.

With his unapologetic style of directing, Lee links America's ugly history with race to the uncomfortable present.

"The whole goal going in was to connect this film that takes place in the '70s to what was happening today and Agent Orange. David Duke, Alt-right, the KKK and the neo-Nazis gave me a coda -- you might say, a wakeup call to end this film," Lee told ABC News’ "Nightline."

“President Trump ... I call [him] Agent Orange, and what is happening in this country is, it’s sad," he continued. "Charlottesville, what happened. And right at that moment, it was crystal clear that I had the ending for the film."

Lee has built his career making overtly political films that delve into the pressing social and racial issues of the day, from "Do the Right Thing" and "Jungle Fever" to "Malcolm X."

His latest film directly addresses President Trump and his initial refusal to renounce hate groups, especially after his remarks following the deadly events in Charlottesville that there was "blame on both sides."

"I did not tell Agent Orange to make that statement about, 'There’s bad people on both sides.' He did that," Lee said. "He was the one who, at a very, I think, a very important point in American history where he could talk not just to Americans, but to the world on hate -- and he sided with hate."

"I believe what he said the first time is what's in his heart," he added. "That's what I believe, because why should there be any debate, any deliberation when you choose between peaceful protesters and hate groups, neo-Nazis?"

"BlacKkKlansman" is a Hollywood take on Ron Stallworth’s book by the same title about his time as a police detective investigating the KKK. Stallworth told “Nightline” how he came up with the idea to infiltrate the Klan.

"I was talking to Ken O’Dell, the local Klan organizer, on the phone and [the idea] just came on," Stallworth said. "[I] told him that my sister had recently dated a so-called 'N-word.' I hate that term, but I said she had recently dated one and every time he put his filthy black hand on her pure white body it made me cringe. And I wanted to do something to stop that abuse of the white race."

Stallworth continued, "His response to me was just kind of man we're looking for when can we meet,” he said. "That’s when I thought, 'Oh hey, what have I gotten myself into? I've got to do something.'"

John David Washington, Denzel Washington's son, plays Stallworth in the movie.

"I was called the N-word by a white person in North Carolina when I was 10 years old, so there's a lot of familiar [feelings],” Washington told "Nightline." "But I have a lot of fun, great memories in North Carolina ... that’s just one.”

Stallworth said he still carries his Klan membership card with him today.

"I have one warped sense of humor," he joked. "If I’m ever in a fatal car crash, some poor cops come up to my mangled black body, go through my personal effects, find that card and just freak out about it."

Because he's black, Stallworth sometimes needed a stand-in for the face-to-face meetings with KKK members, so a white officer agreed to go undercover. For the film, Adam Driver plays his white counterpart. Lee added a dramatic flair by also making Driver’s character Jewish.

During his time with the Klan, Stallworth said he even managed to get David Duke on the phone.

"I've always had a philosophy: Why should I waste time talking to the lowest rung on the totem when I can go directly to the top?" he said. "So if I'm going to call, if I want to deal with 40 acres, I'm not calling some worker bee. I'm calling Spike, you know?"

Over the phone, Stallworth said he and Duke developed a rapport.

"[He was a] very nice conversationalist, very pleasant. If he wasn't who he was, [he could be] the type of guy you would want to sit down and have a drink with, talk about whatever," Stallworth said. "[But] when the subject of race came up, that David Duke, Dr. Jekyll become Mr. Hyde. The monster in him was unleashed and he was off and running."

He said he even paid Duke compliments in those conversations.

"I would tell him how wise he was, how much I wanted to learn to be a Klansman and how I learned ... so much by basically sitting at his knees, symbolically, sitting at his knee," Stallworth added. "He loved this stuff."

Topher Grace plays Duke in the film.

"I remember reading it and thinking, 'I think I've got to take on this character,'" Grace told "Nightline." "I had to go talk to my wife about it for a second ... and she said, 'Why don't you meet with Spike?' And I knew if there was anyone I could do it for ... one person that I could feel comfortable doing it with would be Spike."

Lee did work to make Grace feel more comfortable taking on the role of the grand wizard.

"I wanted to put him at ease. I said, 'Look, no one's going to think that this is you speaking. This is David Duke,'" he said. "And he did a great job. But I understood the trepidation in playing a character like that."

Stallworth himself was impressed by Grace's turn as Duke.

“There are moments in that movie where he looks like David Duke 1978 that I was dealing with," he said, "and he sounds like the David Duke of 1978 that I dealt with it was it was uncanny for me."

If President Trump decided to see the movie, Lee wouldn't mind.

"I’d have no problem with him and David Duke seeing it because they’re in it!" he said. "They’re in the film, and they gave me the ending for the film."

Despite all the dark humor and creative cinematography, the end of BlacKkKlansman is chilling. It's not Hollywood, it's a look at a hard truth.

The film takes a glance back at Colorado Springs circa 1978, but when it turns to Charlottesville the racist cultures that still exist in the nation get a full stare.

This story was featured in Tuesday's episode of ABC News' podcast "Start Here."

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