"Any use of the Guard overseas is fraught with domestic political implications," said Loren Thompson, a military analyst at the Lexington Institute, a Virginia think tank. "The war has grown so unpopular that you have to be concerned if you're in the White House about how voters will react to members of their community once again being called to go fight in a war that to many people seems kind of pointless."
Members of National Guard and reserve units are drawn from the same community, so a large number of deaths in any brigade could have political reverberations.
The most prominent example of how casualties can effect politics occurred in a Marine Corps Reserve unit from Ohio. The company had 23 men killed during its tour in western Iraq in summer 2005, deaths that devastated families across the state.
In the 2006 midterm elections, Republicans lost almost every major statewide office in Ohio, including a GOP-held Senate seat and the governor's office. Polls showed that the Republican losses, particularly in the Senate race, were connected to outrage over the war in Iraq.
The National Guard deployments come after Army officials pushed the Pentagon for more than a year to allow for second Guard combat tours to relieve pressure on the active-duty Army.
Under previous Pentagon guidelines, National Guard units were allowed to spend five years at home after their first combat tours. Gates also revised those rules in January.
The National Guard forces will get bonuses and be activated for a year, meaning they could be in Iraq for as little as 10 months. Previous National Guard deployments to Iraq have lasted as long as 18 months.
Indiana's 76th Infantry Brigade, which was in Afghanistan for 16 months until August 2005, is the National Guard unit that will return to combat the quickest. It will have spent less than 2 1/2 years at home.