There are days when Otis Redding’s posthumous 1968 chart-topper “(Sittin’ On) The Dock of the Bay” sounds — despite all the lame covers and the nearly infinite variety of weirder, or more personally relevant, or simply more contemporary records in the years before and since — like the greatest song ever. Justin Timberlake’s effortlessly suave, polished version at the White House earlier today was exceptional less for the performance than for who witnessed (and joined in on) it. President Barack Obama and First Lady Michelle Obama were both visibly grooving throughout the song, and when The 20/20 Experience falsetto-monger called on them to sing along, the First Couple cheerfully obliged. Unfortunately, although the first hip-hop president has been known to sing now and then, the Obamas’ vocals aren’t audible in the video above. But their broad smiles certainly are visible. And given that even Timberlake rightly acknowledged the tough task of following soul legend Mavis Staples, it’s probably best they saved their pipes for matters of greater national import. What could be of greater national import than “Dock of the Bay,” it’s hard to say right now. It’s one of those days.