Retaking the House, Historical Data

1916: +19/196 (+9.7%)
1924: -24/207 (-11.6%)
1940: -7/169 (-4.1%)
1948: -75/246 (-30.5%)
1996: -9/237 (-3.8%)

These are the numbers from the five cases in the last hundred years when the President's party lost more than 20% of its Congressional delegation in a midterm election and the President's party won the next Presidential election. Specifically these are the changes in the Congressional delegation of the opposition party that had made large gains in the midterm in the Congressional elections that coincided with the Presidential election. To me this is the kind of case to look at to see if the Democrats have a shot at retaking the House next year. There are 242 Republicans in the House; that means the Democrats need to reduce the Republican delegation by 10.3% or more in 2012 to retake the House. Obviously, that happened in two of the five cases I've highlighted. To my mind, that suggests that it's eminently possible, based on scant historical evidence. The Truman performance of 1948 would be serious overkill, and indeed was serious overkill in its own time.

Interestingly, in every single one of these cases the electoral margin of victory for the President or his party was narrower than in the previous election, or only just barely bigger. Clinton went from 370 EVs to 379, but Wilson '16, Coolidge '24, Roosevelt '40, and Truman '48 underperformed Wilson '12, Harding '20, Roosevelt '36, and Roosevelt '44, respectively. So one thing about this data set is that it strongly suggests that Presidents don't take this kind of shellacking in a midterm election and then expand their electoral majority significantly two years later. And Obama probably won't either, unless the Republicans nominate a lousy candidate. But it does make me think that if he does expand his majority significantly in 2012, which seems like a definite possibility (see the part about "Republicans nominating a lousy candidate"), then retaking the House would be just that much more of a possibility.