**John Dickerson**, whose analysis of the candidates' positions on Iraq I've critiqued before, has a short piece up on Slate making the argument that "**McCain **and **Obama** don't think that differently on Iraq." All hail the false bipartisan consensus, I suppose.

The clever formula Dickerson and his co-author **Chris Wilson** use has a couple of errors, but is in fact an excellent tool to prove why the two candidates are so far *apart* on the issue. I'm going to try to do a shoddy reproduction here, but for full effect go look at it at Slate. X stands for conditions on the ground, Y for the size of a residual force, and T for the number of troops. As they point out, to figure out how many soldiers will be left simply multiply the number of troops withdrawn per month, times the number of months and subtract that from the number of troops currently there:

CANDIDATE NAME: NUMBER OF TROOPS - TROOPS WITHDRAWN PER MO. x No. of Months = RESIDUAL FORCE

**Obama**: 140,000 - {2,500-5,000}x * 16 = Y(x)

**McCain**: 140,000 - T(x) * ? = Y(x)

Of course, my equation is a little different than Dickerson's. Since McCain has denied he even used the word "timeline" on MSNBC and his surrogates reject the idea, I'm taking out the more specific number of months Dickerson used (see **Adam**'s post for more on the myth of the secret McCain timetable). In Obama's equation, the only variable is the the conditions on the ground, but Dickerson ignores the fact that Obama is committed to withdrawing troops. If the conditions are good, and the number is larger than one, then of course there will be withdrawal. But for Obama, if conditions are not as good, there is still a commitment and rationale for pulling troops out -- the number approaches zero but never gets there (anyone remember asmyptotes from high school?).

On the other hand, McCain's equation has a lot of variables that his campaign hasn't defined, and no clear commitment to withdrawal. And his most important variable, X, has different parameters than Obama's. McCain's x leans towards being less than zero, since he sees both bad conditions and good conditions as reasons for staying. Now, it is clear both candidates have made ambiguous statements about Iraq (residual force?) and in fact all policy issues, as that is what presidential candidates do. Conditions are going to change by January 2009 and there will be a reaction to them. But in terms of judgment, priorities and strategic inclination, there is a big difference between Obama and McCain on Iraq policy. Pretending otherwise is wrong.

*--Tim Fernholz*