The cost of trying to govern this way has been scorn and derision, not merely from the Republican attack machine, but from those who have fueled the Tea Party movement, liberals and even some pundits who are not known for ideological purity. The 24-hour news cycle, combined with the usual myopia of day-to-day analysis did not help, either.
Another cost--and, I suggest, a greater one--is a loss of message: What do Democrats stand for?
So, should Democrats narrow their big tent and read out some who may seem all but indistinguishable from Republicans? Without Evan Bayh (who has taken himself out of the picture with spectacular bad timing), Ben Nelson and Blanche Lincoln (D.AR), the party would have a lot more intellectual coherence and heft. And if we sent Joe Lieberman to Senatorial Siberia, we'd feel a lot better about ourselves.
While it would be satisfying to have a more coherent party, the genius of American politics was, for many decades, the absence of ideological purity. The broad-based parties of 1950-1980 allowed a huge amount of important legislation to pass; Republican support was crucial to the Civil Rights and Voting Rights Acts. Can we recapture that? Not with Republicans intent on being the Party of No, but would narrowing the range of the Democrats contribute to opening the other party to a more flexible stance? Hard to see how it could.
Still, the most potent forces for changing the present political dynamic are likely to be public pressure--will Republicans be forced to contribute to the nation's governance?--and the self-interest of individual GOP lawmakers; the latter depends on the ability of Democrats to present those across the aisle with opportunities they cannot dismiss and challenges they cannot refuse.
Rather than narrowing the Democratic Party, we need to refine what we are about. We need to do a better job of declaring what it means to be a Democrat (hostility to huge Wall Street banks would be one part). Will that mean that some now members of the party leave? Perhaps, but not necessarily. (What is Olympia Snowe doing in the same party with Jim DeMint and Mitch McConnell?)
Democrats, being a party that makes a virtue of openness and tolerance for differing views, should naturally have a broader membership than Republicans. The challenge is to keep from being so wide-open that we lose all meaning except to win elections, which is a formula for losing them.