Now that the Iraq campaign is winding down, with a new civil (American) administration soon to take over to help the Iraqis build a new government, rationale for keeping American troops in Saudi Arabia becomes weaker.
The Saudi royal family may have cooperated silently with the American campaign in Iraq in return for a promise to withdraw American troops. The troops' presence in Saudi Arabia, home to Islam's holiest sites, is a widespread sticking point in the minds of Muslims. Al Qaeda has stated one of its reasons for being is to get American troops out of Saudi Arabia. They may soon get their wish.
Although US facilities in Saudi Arabia are important and impressive, the US would much rather be in a friendly, democratic country in the region. If all goes well, Iraq may well be that country.
There is no question of removing all trace of American military might from the region. US national security still depends on pressuring Middle Eastern governments into cracking down on terrorist networks. Recent escalation of tension with Syria is an indication of where US policy-makers' attention may soon be turned. Continued presence of American troops in the region will serve as a constant reminder of the peril of defying American will.
American troops will be in Iraq for some time to come, if only to continue the mopping up operations they are currently conducting, rooting out the last remnants of domestic resistance and foreign fighters who entered Iraq during the last stages of the war.
Removing American troops from Saudi Arabia would not only rid al Qaeda of one of its key recruiting points, but it would also allow US-Saudi relations to take a more normal course of development. What shape that relationship would take, without the need for Saudi cooperation to fight a greater evil, provides fodder for interesting speculation.