How strong are American political parties? Party scholars disagree about how to go about thinking about that question. For me, the way to think about party strength is to think about how much of overall political activity goes through the parties. That is, pick an important political activity: writing laws, electing public officials, carrying out laws, political communications, civic rituals, and so on. Pick one, and ask: is it organized by the parties, or by some other mechanism?
So for example, when comparing 1970 with 2010, one would notice that the role of the parties in conveying information is a lot stronger. Back in 1970, most people learned about public affairs through the broadcasts of the three TV networks; if you wanted partisan discussion, you could seek it out from The New Republic or National Review or a handful of other places, but they were clearly on the fringe. Even the (still fairly new) op-ed pages were often filled with the voices from explicitly neutral journalism (in other words, they were more likely to be David Broders and Maureen Dowds, and less likely to be Ross Douthats or Paul Krugmans). Now, of course, we have Fox News and the MSNBC prime time lineup, and left and right blogs, and talk radio, and on and on.
That's the context in which to read Adam Liptak's excellent NYT article about partisanship on the bench. It turns out that clerks for the Supremes are funneled through "feeder" judges, ideologically safe circuit court judges, as part of the way that the legal community sorts itself into two partisan camps. For those interested in how parties work (or, of course, how the Court works), I highly recommend reading the whole article (which also, by the way, appears -- and I don't know the specific literature, so I can't say for sure -- to be an excellent use of academic findings by a reporter). What Liptak doesn't mention is that the same thing he's discussing, which to me is basically the colonization of a new area of politics by the parties, parallels similar takeovers in other areas over the last thirty to forty years. While it's not fully documented, by anecdote it seems to be the case that Congressional staff was once dominated by either non-partisan permanent staffers or by people from the district who were loyal to the boss but otherwise not connected politically. Now, most Congressional staff are firmly embedded in their party's network. The same pattern holds for presidential staff. Nixon's White House contained quite a few people with no connection at all to the Republican Party -- Haldeman and Ehrlichman were pure Nixon men, while Kissinger and Moynihan were Democrats who had worked for other Democrats. Now, White Houses are dominated by career partisans, people such as Emanuel, Messina, Axelrod, and Rouse have had long careers working for a series of Dems. So we have a partisan legislature, a partisan presidency, a partisan court, and a partisan media.
As I hinted there, I see two main forces that rival partisanship in American politics. One is a tradition that can be called neutral expertise, which can be found in things such as civil service laws, the city manager system of city governance, or the Walter Cronkite evening news (and, yes, I know that these things are not "neutral" in the sense of being unbiased, but they are marked by explicit neutrality between the parties). The other is personal loyalty, seen when for example JFK mobilized his family and friends to contest the Democratic nomination for president in 1960. In practice, sorting these things out can be quite difficult. Consider David Axelrod, who worked for lots of Democrats before he ever became involved with Barack Obama, but had also, by the time he reached the White House, a long and deep history with the president. Does he act now "as" a Democrat? As an Obama supporter? As a self-interested political careerist? In some combination of these -- and are incentives and norms established that will encourage those things to coincide? There are quite a few other questions...is a Glenn Beck or a Rush Limbaugh best conceptualized as a Republican, or as an independent entrepreneur, or both? How can we sort out partisanship from ideology -- is a Glenn Greenwald who is quick to criticize Dems who don't follow his public policy preferences "really" a Democrat or "really" a liberal, and how can we understand those distinctions? All of those questions leave party network scholars and scholars of the relevant institutions plenty of work to do. But overall, I think we can at least in broad strokes understand that parties occupy more of the overall political space than they did in, say, 1950-1970, and at any rate we can say that most of what happens in American politics today goes through the parties.
One more thing...it's worth noting some other ways of thinking about party strength that I'm rejecting. I certainly don't think that looking at only the size and activity level of formal party organizations (such as the RNC or DCCC) is the same thing as looking at the larger idea of party strength. Formal party organizations may (or may not be) critical to party functioning, but they've never been the whole story in American parties, and they certainly are not the whole story now. Nor do I think that it's a good idea to judge party strength by the degree to which parties are controlled hierarchically. Indeed -- the fact (as I see it) that Tea Party insurgency against some GOP incumbents is actually an intraparty struggle, featuring people on both sides who have long been involved in the Republican party network, shows just how strong the current party system is. And, to me, party polarization isn't really related to the question of party strength...the parties could differ considerably on questions of public policy but actually not be very central to governing, or they could contain broad overlapping ideologies while monopolizing (that is, duopolizing) all political activity.