Glenn Greenwald breaks it down:
This is what the Democratic Party does; it’s who they are. They’re willing to feign support for anything their voters want just as long as there’s no chance that they can pass it. They won control of Congress in the 2006 midterm elections by pretending they wanted to compel an end to the Iraq War and Bush surveillance and interrogation abuses because they knew they would not actually do so; and indeed, once they were given the majority, the Democratic-controlled Congress continued to fund the war without conditions, to legalize Bush’s eavesdropping program, and to do nothing to stop Bush’s habeas and interrogation abuses (“Gosh, what can we do? We just don’t have 60 votes”). The primary tactic in this game is Villain Rotation. They always have a handful of Democratic Senators announce that they will be the ones to deviate this time from the ostensible party position and impede success, but the designated Villain constantly shifts, so the Party itself can claim it supports these measures while an always-changing handful of their members invariably prevent it.