It was a "fumble," imo, because this was a silly and unrealistic calculation. Why? Because Social Security is still a Third Rail. But this political myopia is not unique to the White House in Washington. Consider Matt Yglesias:
In principle there are lots of other kinds of sequestration rollbacks you could make. You could implement some of the entitlement program cuts suggested in the Obama budget, for example, in exchange for lifting some of the president's least-favorite sequestration elements. Or you could rescind some of the sequestration cuts that Republicans hate most in exchange for rescinding some of the ones the White House deems the most harmful. The Obama team has, probably wisely, not been interested in negotiating with me on this point. But it seems to me that if Republicans wanted to raise some alternative bargains, the White House might need to rethink this.
After all, consider the case of getting liberals to swallow cuts in Social Security benefits. Is the argument "that's the price we had to pay to raise taxes on rich people" really so much more persuasive than "that's the price we had to pay to get a $50 billion infrastructure program to jump-start the economy" or "that's the price we had to pay to start building a universal preschool program"?
Support for Social Security is not a "liberal" thing. It is an American thing. Maybe you could sell Chained CPI in exchange for a $130 billion jobs/infrastructure program to enough liberals to have some working room. The problem is you won't sell it to enough non-"liberals" - can you say "hands off my Social Security?"
There's a reason Pete Peterson, Bowles Simpson, and all the Beltway Elites have been stymied in their attacks on Social Security- it is the most popular government program in history.
The politician who fails to understand this does so at his political peril.