The NYT discusses the voters in the primary elections and makes a prediction about November:
the voters rendering those verdicts will represent only a sliver of the population…Polls show that Republicans are at least poised to erode the Democrats’ House and Senate majorities. But as with the Democrats’ midterm gains four years ago, the uprising will almost certainly be narrow and targeted — not a mass movement.
While primary voters are of course only a portion of all registered voters, the turnout in some states has been considerably greater in 2010 than in recent years. Perhaps the NYT’s prediction about November will be more accurate. We’ll see.