The Democratic leadership may believe--rightly or wrongly--that such a strategy would entail unacceptable political costs. But that's very different from being unable to affect policy. To insist, as many media outlets have, that the Constitution makes it impossible for Congress to stop the war obscures the actual choices facing the nation--by confusing "can't" with "won't."
The political costs to the Democratic leadership that the article refers to, of course, is the capital which is absorbed from those entities that fund their campaigns and ply them with lobbying dollars, not that which is derived from the will of the people. The people can be manipulated with propaganda.
The changes that are needed will run much deeper than simply voting in more Democrats.
Don't get me wrong, I have no problem voting for Democrats. But our system needs changes and safeguards that will prevent our 'representatives' from being so easily corrupted by corporate benefactors.