Tom Jensen identifies the key electoral bloc:

Republicans in Congress are incredibly unpopular. And many of the party's Senate nominees across the country are too. Yet the party is still headed for a big election year. The reason? About 20% of the country is unhappy with both sides- and they're leaning strongly toward the GOP.

Our last national poll found that 19% of voters both disapproved of Barack Obama's job performance and disapproved of the Republicans in Congress. Those folks are planning to vote Republican for Congress by a 76-6 margin this fall. They may not be happy with either side but when it comes to deciding how to vote in November their feelings against Obama are a much more decisive factor than their feelings against Republicans in general.

It's a similar story when we look at Senate races across the country. Voters in Illinois who dislike both Obama and Mark Kirk plan to vote for a Kirk by a 47-9 margin. In California Carly Fiorina's up 69-13 with folks who don't like her or the President. Kelly Ayotte's advantage in New Hampshire is 56-19 with voters who mutually dislike her and Obama. And in older polls we found Sharron Angle up 40-32 in July and Ken Buck up 61-17 in August with voters who meet that description.

I've been banging the drum for a long time about how the combination of a midterm election and a terrible economy makes significant out-party gains all but inevitable. Many analysts, especially those with conservative sympathies, want to paint the electorates mood as a straight ideological judgment: they're voting Republican because they think the Democrats are too liberal. If that was true, you'd see people approving of the Republican Party, at least at higher rates than they approve of the Democratic Party.

That isn't happening. The facts, rather, fit my story pretty tightly: people are angry about the economy, they don't agree with the Republican worldview but they're taking their anger out on the incumbents.