WHEN A SIDESHOW IS EVIDENCE OF SOMETHING LARGER…. As 2010 comes to an end, there are plenty of retrospectives on the year in politics. The Washington Examiner‘s Tim Carney, a conservative, has a worthwhile suggestion this morning for anyone still writing their year-end list.

You might be a self-delusional liberal if … you think Christine O’Donnell was one of 2010’s most important political stories.

That strikes me as more than fair. O’Donnell was a freak show. Her excruciating presence in American politics this year wasn’t meaningful or important — it was a train wreck. A few years from now, most of us will struggle to remember her as anything but “that lunatic who managed to win a low-turnout primary.”

But there’s a flip side to this. As a partial defense of those writing year-end lists and including O’Donnell, I think it’s more than reasonable to note that her primary win was at least part of one of the year’s most important political stories: extremists who won GOP primaries and ended up hurting their party in the process.

Obviously, Republican candidates had a tremendous year nationwide, but in several key contests, GOP primary voters went with radical, borderline-dangerous crazy people, which in turn gave Democrats a much-needed boost. Dem victories in Nevada, Delaware, and Colorado can be directly attributed to the wild-eyed Republican base, which rejected credible, electable frontrunners, only to nominate extremists who lost*. It made the difference between another Congress with a Democratically-controlled Senate, and a chamber with a 50-50 split.

So, sure, I agree with Carney that it’s foolish for any political observer to give O’Donnell, an obvious laughingstock, too much credit. But I’m happy to make the case that one of 2010’s most important political stories was the poor judgment of fanatical Republican primary voters who nominated, among others, maniacs like O’Donnell.

* Update: Dana Houle is right to note that Alaska’s U.S. Senate race fits into the model, even if a Republican ended up winning, given that the party had to invest resources it wouldn’t have had to spend, and is left with a far-less-loyal senator. I suppose we might also put Kentucky in the category, even though Rand Paul won, given that nominating the ridiculous candidate made the race competitive (and expensive), when it wouldn’t have otherwise been close.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.