Washington D.C. -- When Gen. David Petraeus left the Pentagon for the White House Wednesday morning he was unaware that President Obama would ask him to replace Gen. Stanley McChrystal, the now disgraced former commander of the Afghan war. 

After a 45-minute meeting with the president, Petraeus accepted.

But the shuffle leaves a hole at the top of Central Command, or CENTCOM, where Petraeus had the job of overseeing both wars and all other military operations in the Middle East.

So the next big question: Who will fill the shoes of Petraeus in that post?

The answer, according to military officials, is hopefully someone with slightly smaller feet.

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The move is technically a demotion for Petraeus. By accepting the job a commander in Afghanistan, he'll fall one notch down on the chain of command, serving under his own replacement.

It's for that reason, according to senior military sources, the President ought to nominate someone who is proven to work well with Petraeus and is unlikely to usurp his authority.

Two years ago Petraeus was promoted to head Central Command after earning an almost "hero" status within the military community. He's most famously credited for reversing the tide of the war in Iraq and authoring the Army's counterinsurgency manual, now a guiding principle for both wars.

It's widely believed in the Pentagon that whoever the replacement is, he must be prepared to concede some power. "Everybody in uniform knows who's in charge -- and it's David Petraeus," said retired Army Major General Robert Scales.

Military officials say the best fit for the job CENTCOM's current deputy commander, Lt. Gen. John Allen, a name that also appeared on the short list to replace McChrystal. 

"He has the best understanding of what's going on and he has a fantastic relationship with General Petraeus," a senior military official told Fox. "He could move right into that position without any churn to the staff."

Lt. Gen. Allen would be a good fit for many of the same reason's Petraeus was a good fit for Afghanistan. The move could be done quickly with almost zero adjustment period. He knows the people and he knows the mission.

The mission, aside from winning the wars in Iraq and Afghanistan, includes watching Iran. Lt. Gen. Allen has worked closely with Petraeus on that region and could pick up right where they left off.

Other names on the list to take the CENTCOM post in Tampa, Florida include General James Mattis, the head of Joint Forces Command, and Gen. Martin Dempsey, the former acting chief of CENTCOM before Petraeus. Gen. Mattis will be out of a job later this summer when he is scheduled to be replaced by Gen. Ray Odierno.

Meanwhile, President Obama said Thursday the military will "not miss a beat" in the war effort. Hours earlier, Defense Secretary Robert Gates told reporters the he doesn't believe the U.S. is "bogged down" in Afghanistan. "It is slower and harder than we anticipated, Gates said. "But... I think we are moving forward."