Republicans have moved so far to the right and demanded Democrats meet them in the middle. But now, the middle is where the right used to be. That's why Obamacare is Bob Dole's plan from the 90's. Obama's cap and trade was first proposed by George H.W. Bush. The positions that were held by conservatives a generation ago, are now the center-left positions because the right has moved sooo far right.
There really isn't anyone in congress promoting the liberal position on most issues. The public healthcare option was considered "off the table" during the health care debate, let alone single payer. A jobs program? Forget it. Reforming Wall Street? Off the table. Getting out of the Middle East? Off the table. Where is the real liberal or libertarian voice in congress? There isn't one.