But they wouldn’t be the only ones who stay behind: U.S. troops would almost certainly be outnumbered by civilian contractors.

Ever since the U.S. ramped up its forces in Afghanistan in 2007, during the Bush administration, the contracting force has grown at an even faster clip.

In December 2007, there were 25,000 American troops, compared to 36,000 contractors.

In March of this year, the number of U.S. troops stood at about 66,000 — supported by a contracting force of 108,000.

Todd Harrison, a senior fellow at the Center for Strategic and Budgetary Assessments, monitors military spending. “The contractors are there doing jobs to support the troops and those jobs in previous wars were often done by other troops,” he says.