For all you junkies out there, Nate Silver has an interesting breakdown of the GOP wins in NY-9 and NV-2 last night. He uses a broad measuring stick known as the Partisan Victory Index (PVI) to calculate how big a victory was scored. The PVI is "a measure of how the district voted relative to others in the past two presidential elections."
He is warning Democrats that it is beginning to look a lot like 2010:
The Nevada Second, for instance, has a P.V.I. of Republican plus-5, meaning that the Republican candidate would be expected to perform 5 points better there than a Republican might nationally. Since a vote for the Republican is (usually) a vote against the Democrat, you need to double that number to project the margin of victory. In this case, that would imply a Republican win by 10 points given average candidates and a neutral overall political environment.
The Republican Mark Amodei, however, leads by 22 points as of this writing, an easy victory, meaning that he overperformed the P.V.I. by 12 points.
Meanwhile, Mr. Turner's winning margin in the New York district, 8 percentage points as of this writing, represents a 18-point G.O.P. swing from the P.V.I.-projected results.
These numbers contrast with a May special election in New York's upstate 26th Congressional District, a Republican-leaning seat where the Democrat, Kathy Hochul, won. Her 5-point victory margin represented a 17-point Democratic swing from what would be expected from the district under average circumstances.
A lot of volatility out there and the swings back and forth over the last year have been pretty wild. But it's the Democrats who are in big trouble:
In other words, the four special elections, taken as a whole, suggest that Democrats may still be locked in a 2010-type political environment. Democrats might not lose many more seats in the House if that were the case, since most of their vulnerable targets have already been picked off, but it would limit their potential for any gains. And it could produce dire results for the Democrats in the U.S. Senate, where they have twice as many seats up for re-election.
It's certainly possible to read too much into special elections to the House. Over the long run, they have had a statistically significant correlation to the outcome of the next general election. But the relationship is weak and frequently runs in the wrong direction, as it did in 2010.
Good news for GOP freshmen in mostly Democratic districts who would be vulnerable in any case, but appear to have a fighting chance at this point.