President Obama is sending 1,200 National Guard troops to the border with Mexico. This should not be viewed as an innovative solution; Bush sent 1,600 troops to the border under parallel circumstances in 2002. As Ilya Shapiro recently wrote, sending some Guardsmen is no substitute for substantive immigration policy reform.
The National Guard, and the military generally, should not be seen as the go-to solution for domestic problems. Certainly the role they will play on the border will not be as offensive as policing the streets of an Alabama town after a mass shooting (which the Department of Defense found was a violation of the Posse Comitatus Act, but declined to pursue charges) or using a city in Iowa as a rehearsal site for cordon-and-search operations looking for weapons, but politicians from both major parties have at one point or another suggested using the military for domestic operations that range from the absurd to the frightening.
Transportation Secretary Norman Mineta wanted to put Delta Force commandos on airliners after the attacks on September 11, 2001. Air marshals and armed pilots can handle airline counterterrorism; tracking down Al Qaeda organizers in Afghanistan is a better use of Delta’s unique skill-set. Marines conducting counter-drug surveillance near the border shot and killed goat herder Esequiel Hernandez. Something to keep in mind when politicians call for an expanded the role of the military in border security.
Gene Healy’s excellent policy analysis Deployed in the U.S.A.: The Creeping Militarization of the Home Front provides more detail on sensible limits for domestic use of the military. Read the whole thing.