an unanticipated consequence of
Jack M. Balkin
FDR took it 4 times. At this moment, Obama has taken it three times. See http://joshblackman.com/blog/2013/01/20/the-oath-on-a-sunday-and-president-for-a-day/
Eisenhower and Reagan took it three times as well.
As of tomorrow, assuming nothing happens and Obama takes the oath again, he'll be the only two-term president to take the oath four times.