In Rosenberg’s The Day Lincoln Lost (Hanover Square, Aug.), President James Buchanan concocts a scheme to prevent Lincoln’s election in 1860.

What appeals to you about alternate histories?

I have always read a lot of history. My frustration with it has been, at times, that by focusing so intently on what actually happened, it can fail to explore the deeper causes and meanings of events. Focusing instead on what didn’t happen, but might have, allows an author—and the reader—to get away from the ticktock of actuality and dig deeper. That’s the power of a well-done alternative history.

The plot deals with the uncertainty about who would prevail; how likely was Lincoln’s victory?

At the outset, it was highly improbable that he would even get the nomination. Once nominated, it was equally improbable that he could win the presidency simply because there were many more Democratic voters than Republican voters in the country. Then Lincoln got an extremely lucky break: The Democratic Party split, nominating Stephen Douglas as a northern Democratic candidate and then Vice President Breckinridge as a southern Democratic candidate. But even so, a Lincoln victory still seemed unlikely because Lincoln was largely unknown compared to the famous and eloquent Douglas. It was only in the month or two before the election, as many voters became increasingly fed up with the deeply corrupt—and Democratic—Buchanan administration that it began to dawn on people: OMG, the Republican Lincoln might just win!

What did you find was the hardest part of depicting Lincoln?

To try to communicate his sense of humor without telling the jokes he actually told, most of which, when I read them, struck me as not very accessible (or even very funny) to a 21st-century audience. I eventually found a couple work-arounds for the problem, one of which is to have Lincoln always attempting to tell jokes, but being blocked by a judge before whom he’s trying a case: “We’re not going to have any of your jokes in this courtroom, Mr. Lincoln!”

Was writing this book harder than your George Washington alternate history thriller?

I’d say it was harder. Both Washington and Lincoln have high name recognition. But I don’t think most Americans, unless they’re American history buffs, have a particularly detailed knowledge of Washington. With Lincoln, though, I think many people know a lot about things he actually did, like emancipating the slaves. Or what he said. As a result, there’s simply a good deal more well-known material about Lincoln that an author needs to go through to try to get it right.