If there's one man who would seem immune to fear, it's Stephen King, the best-selling author and master of horror fiction.

But after more than 50 novels, hundreds of short stories and numerous film adaptations of his voluminous work, the 69-year-old still gets spooked.

The author's personal boogie man is not a supernatural clown or a zombie, as it turns out - it's Republican presidential candidate Donald Trump.

"A Trump presidency scares me more than anything else," King told Ron Charles, editor of The Washington Post's Book World, during a Facebook Live interview Saturday. "I'm terrified that he'll become president."

King frequently lends his voice - and tweets - to contentious political debates. In recent months, he has also been a vociferous critic of Trump.

In a June interview with Rolling Stone, he discussed Trump as more of a phenomenon than person, calling the real estate executive "the last stand of a sort of American male who feels like women have gotten out of their place and they're letting in all these people that have the wrong skin colors."

He added that Trump's popularity stems from people who desire a world in which there was no question "that the white American was at the top of the pecking order."

During his interview with Charles, King offered a related explanation for Trump's popularity, one that the author appears to understand better than most: fear.

"The key chord to all of this is fear," he said. "We're afraid the government is going to take away our guns, we're afraid that Mexico is going to invade the United States, we're afraid of this, we're afraid of that, we're afraid of taxes, we're afraid of transgender bathrooms - the whole thing."

"As long as people are fearful it's hard to have a rational discussion," he said.

What makes Trump most scary is that he's got a realistic chance of winning the election, the author said.

"I would have laughed three or four months ago, but I think that Trump has a real shot," King told Charles. "I think that Hillary Clinton has been a lackluster candidate, frankly, and there's been a sense of entitlement about her campaign like, 'Ah, it's my turn and I'm running against a buffoon therefore I am already president.'"

King admitted that he's already considered the possibility of moving to Canada to escape a Trump presidency because it "scares me to death." It's not far, he noted, from his home in Bangor, Maine.

Charles asked whether he would write a book about Trump in office.

"No," King replied, "I wrote one called 'The Dead Zone.'"