I know that almost every Democrat, even the ones we think of as most Progressive (Sanders, Weiner, Grayson, Feingold, Kaufman, Franken, Kucinich) all ended up voting for this Health Care law.  No one put their foot down at the very end and said "I vote no.  Really!  I mean it.  No.  This bill is not helpful enough to vote for.  Change it, move it Left, or you WILL NOT have my support."  Given this, it is fair on some level to conclude that we don't have _anyone_ in Congress willing to stand up for Progressive causes like Barbara Lee did three days after 9/11 when she said that the authorization to militarily attack "Terrorists" "was a blank check to the president...to attack anywhere, in any country, without regard to...foreign policy, national security and economic interests, and without time limit."  And so she voted NO and received death threats, accusations of treason, and calls for her removal from all House committees by FOX.  (Yes, I know Lee is still in the House, but that was a decade ago.)

But given the fact that we don't have anyone who is such a staunch Progressive that they are willing to kill Democratic bills for the sake of the (possible) common good, Weiner is about the next best thing.  Small consolation, but true.  He actually does fight, he gets the message out to at least a few MSM-watchers who want to know a bit more about the truth.  And he forces the discussion a tiny bit to the Left, which might be all we can ask for from our death-spiral system and our corporatist media. 

We're going to lose on just about all of these issues anyway, because when the Progressives say no, the Democratic leadership really has no choice (the Republicans will block legislation to the Left of what is currently proposed also).  Advocating for truly Progressive positions might energize the base further (even though we will lose) until maybe something better can be done.  Weiner at least gives us a glimmer of what could be possible.  But you are correct--until the Progressives learn how to say no to the Democratic Center Right, there will never again be a reason for their leadership to move Left.