I won't claim that we have been witnessing something unprecedented, but I'm hard pressed to think of any analogy. We have had presidents die in office, one who resigned in disgrace, but I don't know that we've ever had a president who simply abdicated the way George Bush has. More than that, I'm not sure we've ever had such a shirking of responsibility that has gone without much of an outcry.
George began checking out of the White House, without actually leaving it, after the elections of 2006. After the troop escalation in Iraq early in 2007 he simply referred matters concerning the war to General David Petreaus. Nothing could be debated, discussed or assessed without Petreaus weighing in. For most of 2007, the Decider simply deferred to the General. In other countries they have a phrase to describe what happens in an alleged democracy when a General really runs the show.
A year later, after the economy began to tank, Treasury Secretary Henry Paulson assumed the job of day-to-day president. He briefed the press and hectored Congress. He became the public face of the administration trying to deal with the collapse of markets. W was replaced with Hank.
In his first address after winning the presidency, Barack Obama reminded the nation that we only have one president at a time. He's quite right, but apparently someone forgot to tell Bush. He has blithely punted all the problems he created to the new administration weeks before that administration actually has the power to enact policy.
There is no question that the nation is sick of and embarrassed by George Bush. The Washington press corps left the White House press room for Capitol Hill after the 2006 midterms, and took much of the nation's attention with it. This accounts, I think, for the fact that the 2008 election cycle began so early - we were all so desperate to be done with the Bush fiasco that we wanted to start thinking about his replacement as soon as possible.
Still, Bush's abdication of his job - he was elected for a four-year term after all - verges on dereliction of duty, a Constitutional crisis, small by the standards of the others he has created, but a crisis nonetheless. The nation does only have one president at a time, after all, but now we effectively have none.