The most important congressional primary on Tuesday wasn't House Speaker Paul Ryan's cakewalk in Wisconsin. It was in neighboring Minnesota's 2nd District, where Republicans are scrambling to retain the seat held by retiring Rep. John Kline. Their new nominee: Jason Lewis, a talk radio host who founded an Ayn Rand social network and has a history of making inflammatory comments about slavery and women.

Republicans had fought hard to nominate someone other than Lewis in the swing district, which voted narrowly for President Barack Obama in 2008 and 2012. Kline backed Lewis' Republican opponent, businesswoman Darlene Miller. But Lewis won the district GOP's endorsement and cruised past Miller by nearly 20 points, setting up a November showdown with Democrat Angie Craig. The suburban Minneapolis district is a must-win for Democrats hoping to take back the House, a goal that would require flipping 30 seats currently held by Republicans. That's a long shot right now. But it becomes a bit likelier when the GOP fields controversial candidates like Lewis in swing districts.

Lewis' past comments have been a gold mine for critics. In his 2011 book, Power Divided Is Power Checked: The Argument for States' Rights, he questioned the wisdom of the Civil War, arguing that it had been fought over states rights, not slavery, and changed the nation's constitutional framework for the worse. In his book, he proposed a constitutional amendment that would help restore what he believed had been lost, by allowing any state to peaceably leave the Union. And in a 2011 interview, Lewis declined to say whether the Civil War should have been fought, suggesting, as he had in the book, that there were better alternatives to ending slavery that President Abraham Lincoln could have considered.