It’s almost never good for a political party when one of its incumbent members decides to retire. And yet since human lifespans are finite, nobody can stick around forever. Consequently, it would make the most strategic sense for a party to try to swap out its incumbents when it’s in a position of political strength, so as to ensure that it has the maximum number of not-read-to-retire incumbents in place to help weather the storm. But as Andrew Gelman points out, instead the reverse happens:
As expected, it was a good year for the Democrats, and so it was a logical time for them, as a party, to make some investments in new, young candidates. 2008 was the time they should’ve encourage lots of their incumbents to retire, because in that year they could win a lot of these districts without needing the incumbency advantage (estimated to be about 10% of the vote, i.e., enough to take you from 50% to 60%). Conversely, 2008 was the time for the Republican Party to hold on to what it had, and to keep all their incumbents in, trying to hold out until 2010 when the pendulum might swing back in their favor. But we didn’t see that—actually, something like 30 Republican House members retired in 2008. Republicans retiring, Democrats sticking around—that was a recipe for big Democratic gains. But then in 2010, or 2014, or whatever year it is when the Democrats get wiped out—then a bunch of their incumbents will probably retire, and boy will the Democrats wished they had put in younger incumbents back in 2008 when they had a chance!
It’s not so hard to figure out why this happens. But it’s a reminder that American political parties are somewhat strange beasts. They attract enormous loyalty from millions of followers around the country, but can’t really compel their key personnel to act in the interests of the larger organization.