For the last little while, many Democrats have hoped to avoid the dirty aspects of politics which the Republican Party has mastered, assuming that the fact that most people agree with Democratic positions on a wide range of issues is enough. This, however, hinges on something which Kevin Drum points out doesn't exist:

If we're just going to run on "the issues," we need the media to get that information out to the voters. And if the media have shown us anything in the last five years, it's that they're deathly afraid of "influencing elections." They aren't interested in telling people what party supports what position. If we want to play the politics of contrast, we have to put the contrast out there, and that means slamming Republicans for their positions as well as promoting our own.