An FBI agent goes undercover inside the German-American Bund in Andrew Rosenheim’s Fear Itself, the first in a new historical series.

How did you come to write this book?

It came out of an interest in the under-recognized Germanness of so much of American society; also a “what if” interest about what would have happened had FDR not run for a third term. And spurred by some disapproving English views of America’s comparatively late entry into World War II (I’ve lived in England for about 30 years and so have encountered that sentiment), from my own curiosity about what did take us so long.

And what did?

Much of public opinion was adamantly opposed to entering the war. This had only partly changed after Germany marched through western Europe in the spring of 1940. This isolationist sentiment meant Congress was a very real impediment to FDR’s efforts to engineer an American entry into the conflict. Even FDR, during the campaign of 1940, felt obliged to vow that he would not send young American men to fight in a foreign war.

What led him to consider a third term?

FDR felt he alone could steer America toward war—or least provide effective aid for a beleaguered Britain. He didn’t really decide to run until spring 1940, and did so reluctantly. He knew he wasn’t well; he was deeply fatigued after eight years trying to bring America out of the Depression; and he respected the convention that two terms was enough for any president. But he felt obliged to run, and we should all be glad he did. FDR’s simple courage in wanting to support England and to combat fascism isn’t recognized enough.

Do you see any commonalities between U.S. isolationism at the time and the current reluctance to get involved internationally?

A similar distrust of foreign conflicts in faraway lands, though current skepticism seems more justified, given our recent experience in Iraq and Afghanistan. There is a similar insularity, a similar feeling that the rest of the world can go hang—though this seems rather less justified in today’s very global economy and geopolitics.

Did the book change from its original conception?

The German-American Bund plays a smaller role in the plot that ultimately emerged. The Bund was certainly extremist and ardently pro-Nazi, but it was also largely ineffectual and had withered as a potent political force by 1940. Interestingly, most Bund members were recent arrivals from Germany. German-Americans who had arrived earlier (the vast majority) were never very keen on Hitler, though they were reluctant to see their new country fight their old one.