There is considerable agreement on building up troops in Afghanistan, from President Bush to top military commanders to members of Congress on both sides of the aisle to presidential hopefuls John McCain and Barack Obama.
But without an immediate reduction in U.S. troops in Iraq, an Afghanistan "surge" won't happen anytime soon, according to Pentagon officials.
When McCain and Obama pledge to send more brigades to Afghanistan, they're talking about combat troops. A brigade, or its Marine equivalent, is made up of 3,500 to 5000 troops.
Even if a President McCain or President Obama wanted to send more brigades to Afghanistan tomorrow, he'd have a hard time making it happen.
"The problem is there aren't any units available that aren't designated," says Jack Keane, the Army's former vice chief of staff.
In other words, the Army and Marine Corps are operating at maximum capacity.
Here's roughly how it works: Between the Army and Marines, there are about 50 brigades or regiments â€” teams that do combat operations.
More than a third of these units are now deployed, mostly to Iraq, says retired Gen. James Marks: "Every unit, every BCT [brigade combat team] or maneuver BCT is engaged in the fight in southwest Asia in one way or another. It's either coming from and coming back or getting ready to go to one of those two locations."
The formula for how the Army fields combat units is fairly simple: To send one brigade, it really takes three.
"... You have the unit that's deployed, but you also have a unit that's training to deploy and a unit that's recovering from deployment," says Leonard Wong, a professor at the Army War College in Carlisle, Pa.
This means that even though the Army and Marine Corps have more than 50 brigades between them, only about 18 can be deployed at any given time. Beyond that number would mean longer tours of duty and less time to recover and retrain at home.
Right now, there are about five times more U.S. troops in Iraq than in Afghanistan. So, if the president wanted to beef up the numbers in Afghanistan before the end of this year, he'd most likely have to reduce them in Iraq.
Training Tailored To Site
There are a few complicating factors. For one, says Marks, most brigades getting ready to deploy are training for Iraq. "Now, there certainly is ... what I would call Iraq-specific training and Afghanistan-specific training," Marks says.
If, for example, a brigade was scheduled to go to Iraq this November, the president could simply divert that unit and send it to Afghanistan instead. However, the brigade would then have to extend its training by a few weeks to study Afghanistan-specific intelligence and terrain.
By the time the unit arrived, it would be early December. In that time frame, says Keane, the troops wouldn't have an immediate impact: "It wouldn't be in time for the so-called fighting season that takes place in the spring and summer."
Afghan winters are generally quieter, so Keane believes any possible troop surge in Afghanistan is likely to start in March or April of next year.
For that to happen, Bush would most likely have to reduce or commit to reduce the number of brigades in Iraq before the end of this year.
Keane, who also helped plan 2007's Iraq surge, says there's a risk in doing that, as well. "These are hard-fought gains that we have arrived at in Iraq. We do not want to squander these gains in our haste to move forces to Afghanistan," he says.
But the combination of political pressure and broader public support for the Afghanistan campaign over Iraq means 2009 is almost certainly set to become the year of the Afghan surge.