The most memorable line in Wednesday night's presidential debate, at least if social media is any indication, came when Mitt Romney vowed to cut funding to PBS but added, "I like PBS. I love Big Bird." President Obama had a good comeback for the Big Bird line... except he delivered it a day later.

Reaction to Romney calling out Big Bird was fast and furious on Twitter. The Associated Press reported that tweets mentioning Big Bird were being posted at a rate of 17,000 a minute. A quickly created parody Twitter account, @FiredBigBird, managed to amass about 30,000 followers, despite getting suspended for a while. And a shot of a dejected Big Bird holding a sign saying "Will work for food" circulated far and wide.

But Obama didn't seize on the Big Bird moment until a rally Thursday morning, when, as the New York Times put it, "Obama seemed more energetic than he had the night before." "Thank goodness someone is finally getting tough on Big Bird,” Obama said. "We didn't know Big Bird was driving the federal deficit."

A nice riposte, but it must have left many of the president's supporters wondering where that feisty humor was during the debate itself. There's a great French expression for this sort of delayed response: l'esprit de l'escalier, or "the wit of the staircase." The phrase was coined by the 18th-century polymath Denis Diderot in his Paradoxe sur le Comédien ("Paradox on the Comedian"). As The Yale Book of Quotations explains, "Diderot meant by this the witty rejoinder that one thinks of only after leaving the drawing room and being already on one's way down the staircase."

In their 1906 book The King's English, the Fowler brothers marveled at the compactness of the French expression and argued that there should be an English equivalent (akin to Treppenwitz in German and trepverter in Yiddish):

The French have had the wit to pack into the words esprit d’escalier the common experience that one’s happiest retorts occur to one only when the chance of uttering them is gone, the door is closed, and one’s feet are on the staircase. That is well worth introducing to an English audience; the only question is whether it is of any use to translate it without explanation. No one will know what spirit of the staircase is who is not already familiar with esprit d’escalier; and even he who is may not recognize it in disguise, seeing that esprit does not mean spirit (which suggests a goblin lurking in the hall clock), but wit.

"Wit of the staircase" does indeed get Diderot's expression across better than "spirit of the staircase," and in fact it had already entered English-language literature, even if the Fowlers weren't aware of it. Searching on Google Books, one can find "wit of the staircase" from 1872, in Six of One by Half a Dozen of the Other, a composite novel written by Harriet Beecher Stowe collaborating with five other writers. And the even more concise "staircase wit" appeared slightly earlier, in 1871.

Does "wit of the staircase" work for modern-day political jabs, or is the reference to drawing-room repartee too dated? How about "wit of the next-day rally"? Leave your suggestions for what we should call Obama's belated zinger in the comments below!

Update: On the October 10 Daily Show, Jon Stewart had his own sarcastic take on Obama's "excellent next-day comeback."