For those not concerned about character, the Castle/O'Donnell issue in the Delaware Senate race comes down to a straightforward calculus of electability versus ideology. The implicit argument from some has been that they cancel each other out in this case. Castle is a useless RINO and O'Donnell is an unelectable conservative.
But I would disagree that Castle is a useless RINO, or really that he is a RINO, a "Republican in Name Only," at all. He's a moderate, northeastern Republican. There's a difference.
Look, for instance, at the DW-Nominate metric of congressional ideology developed by Keith Poole and Howard Rosenthal. It's a complicated system to produce a straightforward result: 1.0 is roughly a perfect conservative, -1.0 is roughly a perfect liberal, and 0.0 is a moderate.
Castle has scored a 0.202 in the 111th Congress. That puts him to the right of every Democrat, including Walt Minnick, whom the Tea Party Express tried to endorse. It also puts Castle roughly in line with Jim Gerlach of PA-6 and Dave Reichert of WA-8. The GOP has spent oodles of money in the last few cycles to protect these two, and I do not seem to recall much of a hue and cry that all that cash was going to waste to protect some useless RINOs, and rightly so. They're not RINOs, they're moderates.
Another point about Castle is that Republicans who represent districts in his neck of the woods -- Charlie Dent (PA-15), Gerlach, Peter King (NY-3), Leonard Lance (NJ-7), Frank LoBiondo (NJ-2), Todd Platts (PA-19) -- all tend to cluster around the same ideological position as Castle. And if you look at the 109th Congress, the last time the GOP had a majority and when there were many more northeastern Republicans, you'll see that Castle was right smack dab in the middle of this geographical group of GOPers. This means that Castle is pretty much a mainstream Republican for the Northeast. He's not some extreme RINO heretic. He's just a northeastern Republican.
That points to the bigger issue about Castle: do conservatives want to hold Republican Senate and House seats from the Northeast? If they do, that will generally mean moderates like Castle, although occasionally we will see a conservative like Pat Toomey or a dynamo like Scott Brown. But come on, Scott Brown is clearly an exception to the general rules about all politicians, who tend to be bland, timid, and intentionally boring. You can't bank on a region full of Scott Browns. By and large, genuinely conservative candidates are going to have a difficult time getting elected and staying elected in the Northeast.
That poses a dilemma, one that isn't reducible to a paean to the intrinsic virtues of a "big tent." Instead, the problem is much more practical: with the exception of the once-in-a-while Scott Brown type of candidate (and O'Donnell is clearly no Scott Brown!), the GOP can run moderate Republicans in the Northeast, or it can effectively cede the region to the Democrats, who will elect by default some of the most liberal members in the entire United States Congress. Which is it going to be?
That to me is a choice between half a loaf and no loaf, which is no choice at all. Castle voted against health care reform but for cap-and-trade. The latter vote was maddening. But Democrat Chris Coons would have gladly, eagerly voted for both. And would likely have backed the so-called "public option," too.
Is this really a tough call for conservatives?