The catastrophic 1940 plane crash that killed U.S. Sen. Ernest Lundeen silenced one of the country's leading opponents of American intervention in World War II.

But it wouldn't be long before a sinister claim emerged about the longtime Minnesota politico: He was spreading Nazi propaganda.

Lundeen is the unlikely star of the opening episode of "Ultra," a hit MSNBC podcast hosted by Rachel Maddow that was released last fall. It's about efforts in the 1930s by extremist right-wing elements in the United States, aided and abetted by Nazis, to keep the nation out of World War II and perhaps even install a fascist regime in Washington.

"I've never heard this story, and I pretty much grew up here," she said. "Where was Lundeen from? Was he a spy? What he did — did that have something to do with the plane crash?"

It's a good question, since even the basic facts of the story sound like something out of a screenplay — enough that Steven Spielberg is pursuing a film based on the podcast....