As President Donald Trump pushes the bounds of military activity on domestic soil, a debate has emerged over a nearly 150-year old law that regulates when federal troops can intervene in state issues.<\/p>\n
About 800 National Guard troops filed into Washington, D.C.,<\/a> on Tuesday after President Donald Trump said \u2014 without substantiation<\/a> \u2014 that they were needed to reduce crime in the \u201clawless\u201d national capital. Thousands of miles away, a judge in California is hearing<\/a> arguments about whether the president\u2019s recent decision to federalize Guard personnel in Los Angeles during protests against immigration raids violated federal law.<\/p>\n Trump has also created militarized zones<\/a> along the U.S.-Mexico border as part of a major shift<\/a> that has thrust the army into immigration enforcement like never before.<\/p>\n The cases in both California and Washington mainly hinge on Posse Comitatus Act, which passed in 1878 and largely prevents the military from enforcing domestic laws. Experts say that in both cases there are clear limitations to the law\u2019s enforcement. <\/p>\n Here is what to know about the law. <\/p>\n Posse Comitatus Act stops military from enforcing US law<\/p>\n The Posse Comitatus Act is a criminal statute that prevents the military from enforcing domestic law. It also prevents the military from investigating local crimes, overriding local law enforcement or compelling certain behavior. <\/p>\n Posse Comitatus can be bypassed by a congressional vote or in order to defend the Constitution. The Insurrection Act of 1807 can also trigger the suspension of the Posse Comitatus Act and allows the president to deploy the military domestically in cases of invasion or rebellion.<\/p>\n There is an exception for the U.S. Coast Guard, which has some law enforcement responsibility. The military is also allowed to share intelligence and certain resources if there is an overlap with civilian law enforcement jurisdiction, according to the Library of Congress. <\/p>\n Law was enacted after Reconstruction era<\/p>\n The law was enacted in 1878 following the post-Civil War era known as Reconstruction. Pro-segregationist representatives in Congress wanted to keep the military from blocking the enforcement of Jim Crow laws that allowed racial segregation.<\/p>\n But the spirit of the law also has roots going all the way back to the Revolutionary War, when the founders of the United States were scarred by the British monarchy\u2019s absolute military control, said William C. Banks, a professor at the Syracuse University College of Law.<\/p>\n \u201cWe have a tradition in the United States, which is more a norm than a law, that we want law enforcement to be conducted by civilians, not the military,\u201d Banks said. <\/p>\n That ethos \u2014 ingrained in National Guard personnel starting in basic training \u2014 becomes especially powerful in the case of the Posse Comitatus Act, because the law has hardly been tested before now, said Steve Vladeck, a professor of law at the Georgetown University Law Center. <\/p>\n \u201cThere is no authoritative precedent on exactly where these lines are, and so that\u2019s why over the years the military\u2019s own interpretation has been so important,\u201d Vladeck said. <\/p>\n Law applies to \u2018federalized\u2019 troops<\/p>\n The Posse Comitatus Act typically doesn\u2019t apply to the National Guard because members of the Guard report to the governor, not the federal government. <\/p>\n But when Guard personnel are \u201cfederalized\u201d they are bound by the act until they are returned to state control, according to the Brennan Center for Justice. <\/p>\n