Barack Obama's Facebook photo responds to Clint Eastwood's empty chair

Twitter lit up last night after Clint Eastwood's deeply weird monologue with an empty chair on the prime-time stage of the Republican National Convention.

Today, the White House weighed in with this Facebook post. Looks like the president can take a joke -- or at least go with the flow.

In the middle of all the one-liners, the photo is a stark reminder to Mitt Romney and the rest of us of the power of an incumbent president to set the agenda. The seat President Barack Obama occupies is the center of political action for the whole nation. But it's helpful to remember that this seat, currently occupied by a president well known since childhood for his preternatural cool, can also become a hot seat in a matter of minutes.

World events don't follow our political calendar. In the two months between now and Election Day, a sudden geopolitical surprise, or a nasty weather event that tests the federal government's ability to respond, can make any president squirm in his seat. Those surprises can break a president, or they can give him a chance to be cool, commanding and presidential.

So keep your eye on that chair.