BOSTON — Massachusetts Attorney General Maura Healey is leading a group of 15 Democratic attorneys general in opposing President Donald Trump’s plan to bar transgender individuals from openly serving in the military. The group filed a brief Monday in U.S. District Court for the District of Columbia arguing that banning transgender individuals from the military is unconstitutional and against the interest of national defense and that it harms the transgender community. “Our military should be open to every brave American who volunteers to serve,” Healey said. In the brief, the attorneys general argue that “nothing about being transgender inhibits a person’s ability to serve in the military or otherwise contribute to society.” The brief also argues that Trump made an “irrational decision to reverse recent progress and reinstitute formal discrimination against transgender individuals” and that the administration’s “purported justifications for reinstating the ban are contradicted by research, reason, and experience.” Besides Healey, the attorneys general who signed onto the court brief represent California, Connecticut, Delaware, Hawaii, Illinois, Iowa, Maryland, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Washington, D.C., and Vermont.