The president of the United States is allowed, by law,  to declare a national emergency and call to active duty all the reserve (including National Guard) troops. But only for a maximum of 24 months. The need for troops in Iraq, and for security tasks related to the war on terror, has caused the largest percentage of reserve troops to active duty since World War II. Between 1990 and 2003, some two thirds  of 800,000 reservists were called up at least once, during nine separate "emergencies." But only four percent were called up two or more times. This time around, just about everyone is getting called up at least once. 

For the National Guard, this presents a unique problem; the National Guard are, when not mobilized for federal service, the "armed forces" for the states they reside in. As such, whenever there is a natural disaster, the state governor calls on local National Guard troops for organized, disciplined personnel to help maintain order or assist the victims. This year, some states, like New Jersey, will see 70 percent of their National Guard troops mobilized and sent out of the state. But it turns out that this is not the problem it first threatened to be. State governors rarely mobilize more than 20 percent of their National Guard troops. And if a disaster calls for more than that, neighboring states are usually willing to send some of their National Guard troops. Any nearby federal troops are also made available. But for the first time in over sixty years, the reservists can forget about being a "weekend soldier," although, unlike their World War II grandfathers, they aren't on active duty "for the duration."