Change at the top comes at difficult time for US military
President Barack Obama is re-shuffling his national security team at a time when the resources available to them are diminishing sharply.
The White House wants cuts of $400bn over the next 12 years - and that comes on top of more than $100bn already sheared from the Pentagon budget since this administration came to power.
The outgoing defence secretary, Robert Gates, has warned that the military should not be viewed as the place to solve America's federal deficit problems.
He also made explicit his view that the US should not be drawn into a big military commitment in Libya. Increasingly Mr Gates, a veteran of beltway politics, seems to have surveyed a landscape of growing global turmoil and diminished US resources with a weary resignation.
In a way, the foreign policy elite in Washington (and London for that matter) appears to have divided along the lines of pessimistic apparatchiks and politico optimists.
As a former director of the CIA and defence chief for both Presidents Bush and Obama, Mr Gates personifies the sort of experienced insider who surveys events in the Arab world and can imagine all of the ways revolution in Yemen, Egypt, or Syria could go horribly wrong.
His successor, Leon Panetta, as director of the CIA, it is true, has been exposed to the professional pessimists of that agency for the past few years.
But in his bones he is a democratic party stalwart, and a veteran of many political battles in Congress.
Mr Panetta is more likely to share his president's excitement that the Arab Spring offers an exciting hope of change and renewal than many of the hard bitten case officers he will leave behind at Langley.
If your budget is being cut that deeply, it certainly helps to be an optimist.
General David Petraeus is now widely expected to step into the director's shoes at CIA. He does not fit easily into the category of optimist or pessimist and he is certainly no politician. But having commanded US forces in Iraq, then across the Middle East, and most recently in Afghanistan, assuming along the way a good deal of personal responsibility for the strategy being pursued in those places, he is unlikely to feel that it is all going horribly wrong.
Both Mr Panetta and Gen Petraeus will be moving into their posts at a uniquely difficult time. America's on-off air strikes in Libya have shown how reluctant Washington is to become drawn into new military commitments.
As it becomes clear that the drive to balance the books will mean sitting out crises more often the dangers are clear enough: of waning influence; a drop in military morale; and increasing difficulty in foreseeing which of the many global crises of the next few years will prove impossible for the US to sit out.