Trevor Loudon is no stranger to book sales.

The New Zealand author has sold thousands of self-published books over the years, including 2011’s “Barack Obama and the Enemies Within.”

He also knows books and movies are two very different mediums. And it’s the latter that counts when it comes to public opinion.

It’s why he created “The Enemies Within,” a new documentary tracking an issue he’s been investigating for 30 years – Communist infiltration of the U.S. government.

“A movie is a far more effective way in reaching the masses, a more digestive way to get your message across,” Loudon says.

“The Enemies Within” tracks how Communist sympathizers have gained entry into the U.S. via hard-left elements of the Democratic party. It’s the kind of material you won’t often hear via Rush Limbaugh or conservative outlets like National Review.

“What has surprised us is that some of who we thought were our allies on the right, mainstream conservative media, aren’t willing to touch it,” he says. “It’s too much of a hot potato.” He’s gotten virtual silence from liberals on his movie … so far.

Mainstream reporters like left-leaning Dana Milbank have countered some of Loudon’s observations in the past. Conservative star Glenn Beck has been far more welcoming.

Loudon began tracking this issue in the 1980s when, as he puts it, “radical leftists working through our government destroyed the Australian, New Zealand U.S. military alliance … I investigated the Communist roots of that movement,” he says.

Through the years he observed how popular culture shapes the political system more than most would care to admit. It’s why he created his first film. It also explains how public attitudes toward socialism have shifted over time.

Modern content depicts socialism in a far more flattering light than reality demands, he says.

Liberals routinely insert their ideology into Hollywood narratives, from films and TV shows, he says. And that’s partly why Bernie Sanders’ presidential campaign took hold, particularly with young Americans.

We can partially thank Hollywood for that, he says.

Take “Trumbo,” the 2015 feature starring Bryan Cranston as the blacklisted screenwriter. He was working for a foreign power against U.S. interests, Loudon says. The film’s depiction?

Trumbo was merely a “misunderstood, philanthropic guy,” he notes, according to the biopic. “It does the American public a disservice when traitors are painted as heroes.”

So, if many conservative outlets won’t spread the word about “The Enemies Within,” how will Loudon get people to see his documentary?

He’s planning a college tour following the election.

“We’re gonna make a concerted effort to reach out to the leftists, the moderates, the independents,” he says.