The president may have forgotten something as he boarded Marine One this morning.

On his way to the U.S. Naval Academy graduation ceremony on Annapolis, Md., President Obama didn't return the salute of the marine standing guard at the door of Marine One, as he climbed the steps to the helicopter cabin.

Obama soon ducked his head out, waved to the pilot, and jaunted back down the stairs to address the marine, shaking his hand. In the short video clip, one can't hear the two men talking, so it's unclear what exactly was said. A faint smile appeared to cross the marine's face as the they exchanged brief words.

Obama jogged back up the steps, still not having saluted.

While this exchange may seem to be a military faux pas-Obama typically salutes as he boards Marine One-presidential salutes aren't a fully closed matter. In a 2009 New York Times op-ed, Smithsonian magazine editor and former marine Carey Winfrey identified them as a recent phenomenon, one that evoked mixed feelings from him:

… whenever I saw a president stepping off a helicopter and bringing hand to brow, my drill instructor's unambiguous words came back to me with much of their original force.

Then there were the salutes themselves, which ranged from halfhearted to jaunty. None of them fulfilled the characteristically succinct prescription that Capt. Jack O'Donnell of the Marine Corps delivered, in 1963, to my platoon of freshly minted second lieutenants at basic school in Quantico, Va.: "Your salute," he pronounced, "must be impeccable …

Presidents have long been saluted, but they began returning salutes relatively recently. Ronald Reagan was thought to be the first, in 1981.

Reagan, Winfrey wrote, consulted the Marine Corps commandant on whether saluting back was appropriate. Marines themselves are taught not to do so out of uniform, and Winfrey raised the obvious point: Presidents, in suits and ties, aren't wearing uniforms. But as commanders in chief, they're in charge, and according to the advice Reagan got, supersede the protocol.

So while Obama typically does salute, it's not as if he's required to.