Over the last few weeks, Barack Obama and John McCain have seemed to get perilously close to agreeing on what to do in Iraq. Obama continues to talk about a 16-month withdrawal but would let military commanders determine the pace of the withdrawal. McCain is also now in favor of a 16-month timeline—as long as the commanders determine the pace of the withdrawal. After the withdrawal, how many soldiers would be left and what would they do? Both candidates agree on that, too. U.S. forces would continue to train Iraqi soldiers, fight al-Qaida, assist Sunni tribal leaders, and fight Shiite militias. How long they would do all of this, and in what numbers, would be up to the commanders on the ground.

How close are the two candidates? Below are two mathematical formulas derived from their public statements. Mouse over each number and variable to see the source.

X.Advice from commanders: If conditions improve, X will equal 1 or greater, Obama will bring one to two brigades home each month, and McCain will complete the withdrawal in 16 months. (One brigade=2,500 troops.) If the military advisers recommend a less expeditious withdrawal, X decreases, the number of troops that Obama withdraws each month lowers, and McCain's overall timetable expands. The residual forces both candidates envision (which are a function of X) will also get larger.

Y.Residual Force: The result of the equation equals the number of U.S. soldiers who would remain in Iraq to continue to train Iraqi soldiers, fight al-Qaida, assist Sunni tribal leaders, and fight Shia militias.