I predict that one day, future political humorologists will look back at Election 2012 and identify the precise moment when one presumptive presidential nominee launched the first effective on-message joke against the other. They will be scrolling through some old C-SPAN footage of President Barack Obama’s remarks at the Associated Press luncheon and get about 19 minutes in when he says these words:

“One of my potential opponents, Governor Romney…said that he’s very supportive of this new [House Republican] budget. And he even called it ‘marvelous’—which is a word you don’t often hear when it comes to describing a budget.”

The tape will reveal that an audience of editors and journalists responded to this gentle jibe with a tittering of laughter, which visibly pleased Obama. In fact, from the delighted expression on his face, it seemed to set off an interior monologue that you can just about hear. (At least I can.)

They laughed! Of course they laughed! ‘A marvelous budget?’ Who talks like that—Gov. Thurston Howell III? Mitt might as well have called it the ‘bee’s knees.’

Just then a sudden smirk indicates that the president has arrived at a funny thought, setting internal editing sensors on Red Alert. He thinks: Do I say it? Dare I say it? Oh my God—I think I’m gonna say it…

Then he says it: “...It’s a word you don’t often hear generally.”

Paydirt! With that joke and the loud laughter it elicited, Obama effectively underscored Romney’s status as “Other.” And what a delicious irony it was. In this week of Campaign 2012, when many savvy pundits were pointing out how Romney projected his own vulnerabilities upon Obama (Out of Touch! Flip-flopper! Medicare-cutter! Harvard elitist!), the President found a way to tattoo Mitt with the very same characteristic which the right wing has tried to pin on Obama: otherness. To the careful listener, the president’s joke asked the question: Hey Karl Rove, how does otherness feel on the other foot?

Which is why this remark is worth watching again and again, in slow motion, frame by frame, Zapruder-style. To me, it reveals an inspired joke conceived, evaluated and expertly delivered, all in real time. Even if the entire routine was fully scripted, Obama deserves applause for a presidential acting performance the likes of which we have not seen since the days of Ronald Reagan.

Mostly, the remark reveals a president at the Ultimate Moment of Decision about whether or not to launch a strike against his opponent’s greatest liability: Mitt Romney’s seeming inability to relate to the 99%.