Here’s Paul Krugman last week in The New York Times, urging Barack Obama “to draw a line in the sand” regarding the debt ceiling issue:

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. They believe that they have the upper hand, because the public will blame the president for the economic crisis they’re threatening to create. In fact, it’s hard to avoid the suspicion that G.O.P. leaders actually want the economy to perform badly.

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. It’s time — indeed, long past time — for him to prove them wrong.

It’s good advice, but Krugman, like many other observers, is watching this Obama comedy play out with a sinking feeling that the president is about to fall off a cliff and take Social Security and Medicare with him rather than call the GOP’s bluff on its threat to vote against raising the debt ceiling.

Obama’s die-hard supporters think he’s backing up to ensure himself a second term, by painting intransigent Republicans as extremists. It’s Bill Clinton-style triangulation all over again, they say. Sounds good until you consider what this means to the rest of us. By messing with entitlements and not calling for substantially higher taxes on the rich, Obama only proves there’s not a dime’s worth of difference between the major parties.

In the old Warner Brothers cartoon, Bugs Bunny draws a line in the sand and dares Yosemite Sam to step over it. Sam does so and Bugs, backing up, draws another. He keeps drawing lines and backing up until he fools Sam into stepping off a cliff.

Except that in the modern-day cartoon of D.C. politics, it looks like Bugs (Obama) is the one who will take the fall. He’s not fooling anyone. If he caves on the cornerstone programs of America’s social safety net, especially in our rapidly worsening economy, there’s nowhere for him to go but down.