Obama responded with a recent history of government spending. Then Letterman went back to the tally: “Now, do you remember what that number was? Was it $10 trillion?”

Then came the payoff, as the president made clear that he really didn’t want to utter the word “16”: “I don’t remember what the number was precisely.”

No daylight for the fact-checkers there: Since the debt is moving so fast, precise recollections are all but impossible.