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Looking Ahead to 2010 Elections, Part 1

Before launching into my first post here at 538, let me say two things. First, it’s an honor to guest-post here, especially given the quality of content produced by the regulars and my fellow guest-bloggers this week. Second, I am going to dedicate a series of posts toward previewing the 2010 elections, some based on the Partisan Voting Index data compiled by POLIDATA, the National Journal and the Cook Political Report.

PVI refers to the House district-level partisan performance of presidential candidates. For example, in 2004 John Kerry carried 179 districts. He also won 19 states plus the District of Columbia. If the other 48 states used the electoral vote allocation formula only Maine and Nebraska do—that is, two electors for the statewide winner and one for winner of each House district—Kerry would have amassed 38 electors for his 19 states, plus 3 for DC, plus 179 for the districts he carried, for a total of 220 electors. He instead won 252.

That suggests that there was either a lot of split-ticket voting for George W. Bush and Democratic House candidates, or Democrats have their core supporters over-packed into too few districts. In the final chapter of my book, Whistling Past Dixie, I demonstrated that the latter was a key factor, in part because race-minded redistricting produces certain districts with overwhelming Democratic majorities, inefficiently so for Democrats.

The district borders will be in place for one more cycle, so this disadvantage still pertains. But district demography and voting patterns can change. That’s obviously true, given that the Democrats captured enough seats in 2006 to form a majority from the same set of district lines Republicans forged a majority in 2002 and 2004.

All that said, what can we say about the House-level results in 2008?

Taking a first cut at the data, the overall results show that:

  1. Of the 435 districts, 352 were carried by the same party as the presidential candidate. Barack Obama and the Democratic candidate won 208 of those, and John McCain and the Republican candidate won the remaining 144.
  2. That leaves 83 districts with cross-partisan results—what POLIDATA calls McCain Democrats (MD) or Obama Republicans (OR). There were about half again more of the former (49) than the latter (34).

This suggests Republicans have a slight overall advantage, because there are fewer districts held by Republican House members in which Obama’s performance potentially indicates GOP vulnerability, rather than the reverse. Obviously, as a party’s House majority widens, as was the case for Democrats between 2006 and 2008, the number of potentially winnable targets tends to shrink and the number of potentially marginal seats to defend grows, all else equal.

But all else may not be equal. Counting districts simply as “McCain Democrats” or “Obama Republicans” does not indicate either the margin of victory for those incumbents or the opposite party’s presidential candidate. Nor does it consider idiosyncratic factors like state and local politics, and the strength of individual incumbents.

I’ll drill down into that a bit more in subsequent posts.