Dave Wasserman of the Cook Political Report notes that of the 60 House races he deems potentially competitive, 45 are in districts currently held by Democrats.

While I can’t begrudge a Republican for smiling at that news, it’s pretty much what one would expect in a Congress that has a lot more Democrats than Republicans. In 2006 and 2008, Democrats won just about every seat that could be considered “low-hanging fruit.” There are a few pickup opportunities left, but they mostly represent seats where a Republican won in unique circumstances (Joseph Cao in New Orleans) or open seats (Mike Castle’s seat in Delaware, Mark Kirk’s seat in Illinois, Jim Gerlach’s seat in Pennsylvania).

Meanwhile, the vulnerable Democratic seats come in bunches and can be classified in different categories. You have a couple of retirements and open seats created by folks running for higher office, like John Tanner in Tennessee, Dennis Moore in Kansas, Joe Sestak in Pennsylvania, and Paul Hodes in New Hampshire.

You’ve got your perennial at-risk Democrats who have hung on because of the party’s momentum in recent cycles, like Jim Marshall and John Barrow in Georgia, and Allan Mollohan in West Virginia.

You’ve got a couple of how-did-a-Democrat-win-that-Republican-leaning-seat outliers, like Walter Minnick in Idaho, Parker Griffith and Bobby Bright in Alabama, and Frank Kratovil in Maryland.

You’ve got states where the Democratic brand is rapidly being damaged, usually with an unpopular incumbent governor: New York, Pennsylvania, New Jersey, North Carolina, Ohio, Michigan, Colorado.

You’ve got the-mouth-is-a-time-bomb incumbents like Alan Grayson in Florida, and perhaps Steve Kagen in Wisconsin and Carol Shea-Porter in New Hampshire. If Baron Hill keeps acting like his first name is a title, maybe he could be tossed on this pile, too; the reaction to the town meetings elicited a lot of “I don’t answer to you rabble” comments from Hill that could make good ad fodder next year.

The most dominant theme I’m seeing are states where Republicans did well in the first part of this decade, but where their candidates collapsed as President Bush’s popularity tumbled further and further: New Hampshire, Virginia, Ohio, Colorado, Nevada, New Mexico, Iowa. (Unsuprisingly, these are the states that have switched from red to blue between 2000 and 2008.) Anger, frustation, and exhaustion with Bush drove a lot of Democrats to victory in 2006 and 2008, making a lot of states look bluer than they really are, if this year’s elections are any indication.

What does this mean for Republican hopes for the House in 2010? A lot of the groundwork has been laid, but there’s still a long road ahead; getting anywhere near the 40 seats needed would require a big wave and almost everything bouncing their way.