Donald Trump has signed an official White House directive banning all transgender individuals from serving in the US military, the Pentagon announced yesterday.

By Nathan James

The 3 PM edict, delivered to the Defense Department shortly after Trump affixed his name to the document, makes the President’s Tweets earlier this summer, military policy. A White House official, speaking on condition of anonymity, cited security as the basis for the President’s action. “This policy is based on a series of national security considerations,” he said, noting that the policy also ends medical treatment procedures for transitioning service members. “We have not yet worked out how existing transgender troops will be handled under these guidelines,” the White House official said, adding that the service chiefs would have “latitude” in formulating implementation of the order.

This move reverses former President Barack Obama‘s decision to allow trans men and women to serve openly, and for the armed forces to begin accepting transgender recruits this year.

The policy change affects up to 15,000 transgender soldiers, sailors, and aviators currently on active duty or in the Reserves. The White House declined to specify whether the affected troops would be discharged honorably or otherwise, a distinction that could profoundly impact their civilian lives. Other-than-honorable discharges, according to military experts, can result in denial of VA medical care, or employability.

The new marching orders, which will be administered by Defense Secretary James Mattis, are based on a series of Tweets Trump made last month. “After consultation with my Generals and military experts, please be advised that the United States Government will not accept or allow transgender individuals to serve in any capacity in the U.S. Military,” Trump wrote. “Our military must be focused on decisive and overwhelming victory and cannot be burdened with the tremendous medical costs and disruption that transgender in the military would entail.”

The edict contradicts a June 2016 Rand Corporation study that found trans troops serving openly in the military had “minimal impact” on overall unit readiness. An earlier study by then-Chairman of the Joint Chiefs Adm. Mike McMullen started that “military readiness improves when the troops are allowed to be who they are.”

The Veterans Administration estimates that, of the Defense Department’s $5.4 billion healthcare expenditure, transgender medical treatments cost between $2.4 million and 8.4 million a year, an “exceedingly small” portion of the overall budget.

Trump, however, made the Tweets citing cost and unit effectiveness, without meeting with the Joint Chiefs on the issue, Pentagon leaders said. “General Mattis was actually on vacation at the time of the President’s Tweets,” said Commander Thomas Kincheloe, a Pentagon spokesman. Two advocacy groups–the American Civil Liberties Union, and OutServe/SLDN, say they plan to sue the Trump Administration over the ban.

One service chief, Admiral Paul Zunkunft, commanding the Coast Guard, vowed “not to break faith” with the transgender sailors serving under him, saying “all of them are doing meaningful Coast Guard work.” Observers note that in light of Trump’s new policy, those remarks will likely end Zunkunft’s career.