Sullivan thinks the Stewart/Colbert moment will ebb:

This moment will pass, of course. One gets a sense that it may be peaking already. For satire to work well, it has to let off the collective steam of a nation. It needs a po-faced, Cheney-style establishment to mock. As the religion-drenched era of Republican hegemony wanes a little, the satirists begin to become part of the establishment themselves. Colbert’s presidential run may be a step too far. Perhaps, in retrospect, these last, ragged months of the Bush administration will come to seem the high-water mark of the Colbert-Stewart tide. But it’s been a joy while it’s lasted.

Al Franken's mock presidential run was a publishing stunt too far, if you recall, which you probably don't.