Nate Silver believes that the GOP is reprising Howard Dean's 50 state strategy:
According to research by Derek Willis of The New York Times, the Republicans will nominate candidates in 428 Congressional districts this year, leaving only seven races all in overwhelmingly Democratic areas, like the South Side of Chicago uncontested. This contrasts sharply with 2006, when Republicans left the Democrats unchallenged in 45 districts, or 2008, when they failed to nominate a candidate in 42 races.
The Democrats, for their part, are not doing badly: They will have a candidate on the ballot in 412 districts all but 23 which is better than their recent historical average. Still, this is a step down from 2008, when they left just 14 seats uncontested.
He gives Republicans about a 25 percent chance of taking over the Senate.