The committee reserved $3 million in Minneapolis, where Democrats could shore up Rep. Tim Walz (D-Minn.) or attack Reps. John Kline (R-Minn.), Sean DuffySean Patrick DuffySean Duffy, Rachel Campos-Duffy expecting their ninth child Cheney's advice to daughter: 'Don't screw it up' Senate bill seeks to bring freedom back to banking MORE (R-Wis.) or Chip Cravaack (R-Minn.).

The rest of the list of potential targets reads like a who's who of Republicans that Democrats have made clear they hope to knock off in November: Florida Reps. Vern Buchanan, Steve Southerland, David Rivera and Allen West; Iowa Reps. Steve King and Tom Latham; and Colorado Reps. Mike Coffman and Scott Tipton.

Democrats also could use the airtime to defend their own vulnerable incumbents, including North Carolina Reps. Mike McIntyre and Larry Kissell.

"House Democrats are beginning the 2012 election season on defense," said National Republican Congressional Committee spokesman Paul Lindsay. "Why? Because many of their members are in strong Republican seats where they will be forced to defend their party’s singular focus on ObamaCare while America’s economy has gone from bad to worse."

In previous cycles, the DCCC's earliest buys were in May or June, according to the group.

By purchasing the airtime in "combo" blocks market by market — rather than race by race — the DCCC can leave Republicans guessing about who they will target and how much they will spend on each ad up until the ads are ready to air, an official said.

The DCCC's independent expenditure arm cannot coordinate directly with Democratic candidates.

- This post was updated at 3:27 p.m.