WASHINGTON – It is encouraging that President Obama, at least on foreign policy matters, still has the ability to surprise and impress.

The only real objection to the sacking of Gen. Stanley McChrystal following his spectacular collapse of judgment was the delicate nature of the moment in Afghanistan itself. The Afghan surge is just getting up to strength. Large exertions are ahead. A disruptive command change, at this point, would have left Obama open to the charge that his offended pride was more important than ongoing military operations.

There was only one choice that could have vindicated presidential authority over the military while ensuring the continuity of operations in Afghanistan – and Obama made it. Gen. David Petraeus is the intellectual architect of modern counterinsurgency strategy. He is revered by American troops and trusted by Afghan President Hamid Karzai. Most urgently, Petraeus knows how to show deference to civilian control of the military without abandoning his own military views.

By agreeing to serve where the need is greatest, Petraeus assumes a reputational risk. But his appointment must also involve a pleasing sense of vindication. Just three years ago, a trio of Democratic senators named Clinton, Biden and Obama gave Petraeus a hostile reception on Capitol Hill. Petraeus’ report on improved conditions in Iraq, said Sen. Hillary Clinton, requires “a willing suspension of disbelief.” “We should stop the surge and start bringing our troops home,” argued Sen. Joe Biden. Progress in Iraq, said Sen. Barack Obama, is “considered success, and it’s not.”

It is now officially impossible for Democrats to downplay the dramatic, historic achievements of the Iraq surge, having turned to its author in their own time of need.

By accepting Gen. McChrystal’s resignation, Obama aims at “unity of effort” across his national security team. But the cause of disunity was not McChrystal and his staff alone.

The Obama administration’s 10-month Afghanistan policy review last year will be long-remembered as an example of botched executive decision-making. After a false start that resulted in no consensus, even in the president’s own mind, Afghan policy process 2.0 was dominated by a civilian-military disagreement that produced a steady supply of press leaks and the unauthorized release of classified documents. Staffers within the White House and the military took up cudgels on behalf of their principals, with little of the restraint shown by the principals themselves. Arguments became camps. A team of rivals ceased to be a team at all. And the process never seemed to end.

In December, Obama announced an expanded mission in Afghanistan to be achieved on an 18-month deadline. The military interpreted that deadline as aspirational – a way to pressure the Afghan government into assuming greater responsibility while keeping future military options open. White House officials saw the deadline as hard and fast – a way to reassure restive Democrats on Capitol Hill and eventually get out of a messy conflict, no matter the outcome. This ambiguity carries a danger – that the Taliban will think America can be outlasted or forced into desperate deals that betray the Afghan people.

On Afghanistan, Obama seems genuinely conflicted. As a foreign policy pragmatist, he understands the unacceptable strategic costs of American failure in the extremist heartland. As a former anti-war senator and the peace candidate in the last election, he cannot bring himself to fully commit to an unpopular war. So he has told the military, in essence: We will give you more resources but limited time. This formulation, however, involves an inherent division between “us” – a White House with limited patience – and “them,” a military that would be blamed for failure. This is a typical pose for Congress, demanding results from the military in exchange for additional time and resources. It is not a typical attitude for a commander in chief, who normally identifies more closely with the fate, views and goals of the men and women at his command.

Does the appointment of Petraeus resolve this ambiguity? It certainly lessens it. Testifying in Congress last week, Petraeus said, “it is important that July 2011 be seen for what it is, the date when a process begins based on conditions, not the date when the U.S. heads for the exits.” The selection of Petraeus can only be seen as an endorsement of this view.

But it is another, necessary act of leadership for Obama to end this ambiguity in his own voice.

© 2010, Washington Post Writers Group