Ezra Klein emphasizes an obvious fact: a deficit deal isn't worth anything "if it’s not honored by future Congresses":

[T]he question can’t just be whether we can make hard decisions this year and write a big bill that allows us to pat ourselves on the back and say we solved the deficit problem. The question has to be what processes and policies are we putting into place that make it easier for future Congresses to stick to the fiscally responsible laws we put on the books. In the end, real deficit reduction is a decades-long commitment, not a vote and a press conference.

Sure, but an epic attempt to solve the problem now, if endorsed by the political middle, will have long-term ramifications. And the sooner we start, the less crushing will the debt eventually be.