In the Boston Review, Stephen Ansolabehere and James Snyder write that the tea party movement has been overrated:
It is tempting to believe that the Tea Party endorsement moved voters. Indeed, the candidates endorsed by these groups did well: 64 percent of Republican candidates endorsed by the Tea Party Express or FreedomWorks (or both) won, while only 52 percent of non-endorsed Republicans won. The numbers look even more impressive among non-incumbents: almost 52 percent of endorsed candidates won, while only 28 percent of non-endorsed candidates won.
But the tea party groups mostly endorsed candidates in heavy Republican districts who were going to win anyway. If you take a look at the vote percentage of tea party candidates (shown with black Ts in the chart below), it looks pretty similar to the vote percentage of all the other Republican candidates:
This seems pretty plausible, especially since it matches what seems to have happened in the Senate, where tea party candidates didn't do any better — and might even have done worse — than other Republicans. On the other hand, I think it's possible that this might miss what happened in the primaries, where tea party endorsements helped power conservative candidates to victory over more moderate ones. That doesn't show up in the general election results, but it's a real effect nonetheless.