US Department of Defense: Chuck Hagel (Secretary of Defense)
Why this was a big quit:
The United States of America boasts the most powerful and sophisticated military machine in the history of mankind. So when its Secretary of Defense quits, as Hagel did in November, it is a big deal, regardless of whyit happened. His resignation came on the heels of the loss of the Democratic majority in the Senate following the Midterm Elections.
Why this is not as big as our Top 10:
Hagel was hired for a different skill set than is now required to deal with the threat from dispersed radical terrorist groups. Hagel was going to reduce and reorganize the DoD, not deploy new campaigns. Considering that, it is hard to consider that the Pentagon will be worse off going forward without his kind of expertise.