For his Friday column, Paul Krugman expands on his previous thought that if Obama caves again, his “presidency is over” (my emphasis):

So failure to reach a debt deal would have very bad consequences. But … Obama must be prepared to face those consequences if he wants his presidency to survive.

Bear in mind that G.O.P. leaders don’t actually care about the level of debt. Instead, they’re using the threat of a debt crisis to impose an ideological agenda. … So what’s really going on is extortion pure and simple. As Mike Konczal of the Roosevelt Institute puts it, the G.O.P. has, in effect, come around with baseball bats and declared, “Nice economy you have here. A real shame if something happened to it.”

And the reason Republicans are doing this is because they must believe that it will work: Mr. Obama caved in over tax cuts, and they expect him to cave again. … Republicans believe, in short, that they’ve got Mr. Obama’s number, that he may still live in the White House but that for practical purposes his presidency is already over.