According to the S&P, who as you might recall are responsible for it, Republicans are to blame.
We have changed our assumption on this because the majority of Republicans in Congress continue to resist any measure that would raise revenues, a position we believe Congress reinforced by passing the act.
But don’t expect to hear much of that on the TV box.
EDIT: the above is in specific relation to the Bush Cuts expiring, but the overarching point from the report (which you can read here), is that the spending cuts won’t make a dent on the debt without revenue increases, and although they aren’t endorsing anything per se, cuts alone aren’t solving the problem.
Let it never be said that old Hanlon won’t check his work.