Brendan Nyhan acknowledges that the budget deal was shockingly tilted toward GOP priorities. His explanation is that politicians overreact to the effects of wave elections:
Over the years, I've frequently invoked the pioneering research (PDF) of UNC's Jim Stimson and his co-authors on responses to perceived "mandate" elections, which shows that members of Congress tend to deviate from their normal voting patterns in the direction of the election result for some period of time. Stimson was quoted yesterdaysaying that this election did not meet the definition of a mandate:
"[The GOP is] right to be nervous about [the Ryan plan]," said James A. Stimson, a University of North Carolina political scientist and a co-author of the recent book "Mandate Politics." By his measure, the resistance of Democrats who still control the White House and Senate means Republicans cannot claim a mandate any more than Mr. Obama could upon taking office in 2009.
It's true that the 2010 election results have not been accepted as a mandate by both parties like 1964, 1980, and 1994 (the post-WWII cases Stimson and his colleagues identify). In this sense, 2010 was more like 2006 or 2008 than 1994. However, as I'vesuggested before, it's not clear that both parties will ever accept mandate claims in the way they previously did given the level of polarization that now exists. In this sense, 2010 may be something of a "soft mandate," empowering Republicans and pushing Obama and the Democrats to accept deals they otherwise would not have considered. Imagine a world in which Republicans kept the House in 2008 and maintained control in 2010, but the Senate and presidency were configured the same way they are today. Would the GOP have been able to pull off that deal? I'm skeptical.
But you didn't see Republicans reacting this way to the 2006 and 2008 wave elections, did you? Quite the opposite, in fact.