Amidst all the hullabaloo about debt ceilings and grand bargains, the one thing liberals should be most concerned about is: can Obama win in 2012? Republicans have notoriously said their goal is to make Obama a one-term President. That's honest. By the same token, the goal for liberals should be to make Obama a two-term President.
A one-term Presidency means the probable loss of most of the liberals gains of the past 2 1/2 years (though it'd be interesting to speculate on which are most vulnerable). It means the Supreme Court gets more conservative justices and fewer liberals. It means years on the defensive, being hypocrites as the Dems in the Senate use the threat of filibuster in a delaying action against President Romney. It means the reopening of the debt limit deal to add further tax cuts and further spending cuts.
A two-term Presidency means protecting the liberal gains, and with the opportunity to make more gains. It means the possibility of new liberal blood on the Supreme Court. It means the reopening of the debt limit deal to tweak the tax system (think of the changes to the welfare reform that Clinton got through in subsequent years).