When Julia Jones arrived at her office in Santa Monica at 8 a.m. — by Hollywood screenwriter standards, the crack of dawn — she found Stephen K. Bannon already at his desk, which was cluttered with takeout coffees. They were co-writers on a Ronald Reagan documentary, but Mr. Bannon had pretty much taken it over. He had been at work for hours, he told her, writing feverishly about his political hero.

Today, with Donald J. Trump, whose election Mr. Bannon helped engineer, on the threshold of power, the 2004 film “In the Face of Evil” has a prophetic ring. Its trailer has an over-the-top, apocalyptic feel: lurid footage of bombs dropping on cities alternating with grainy clips of Reagan speeches, as a choir provides a soaring soundtrack. The message: Only one man was up to the challenge posed by looming domestic and global threats.

“A man with a vision,” the trailer says. “An outsider, a radical with extreme views.”

The Reagan presidency has been a recurring touchstone for Mr. Bannon since 1980, when as a 26-year-old Navy officer he talked his way into Mr. Reagan’s election night celebration. It was at an early screening of “In the Face of Evil” that he met fellow Reagan admirer Andrew Breitbart, the budding conservative media provocateur.

Breitbart.com’s scorn for Muslims, immigrants and black activists drew a fervent following on the alt-right, an extremist fringe of message boards and online magazines popular with white supremacists, and after Mr. Bannon took control of the website in 2012, he built a raucous coalition of the discontented.