A 2014 study by the Williams Institute at the University of California, Los Angeles, estimated that about 8,800 transgender people were serving on active duty, with thousands more in the National Guard and reserve; a 2016 study by the RAND Corporation estimated that there were about 2,450 such active-duty troops.
In 2016, the Obama administration, after extensive study, lifted a prior ban on transgender troops. That permitted transgender members currently serving to come out openly; openly transgender people are set to be allowed to join the military starting next year.
But on July 26, without warning, Mr. Trump stated on Twitter that the government “will not accept or allow transgender individuals to serve in any capacity in the U.S. Military.” The announcement caught the military off guard, and there was no plan for what to do about those now serving openly.
Gen. Joseph F. Dunford Jr., the chairman of the Joint Chiefs of Staff, responded to Mr. Trump’s tweets by saying that the current policy about who was allowed to serve had not changed and would remain in place until the White House sent the Defense Department new rules and Jim Mattis, the defense secretary, issued new guidelines.
“In the meantime, we will continue to treat all of our personnel with respect,” General Dunford said in a letter to the military service chiefs.
On Aug. 4, The Blade, a newspaper for lesbian, gay, bisexual and transgender people, reported, citing unnamed sources, that a policy guidance for reinstating the ban had been approved by the White House Counsel’s Office and by Mr. Trump and was expected to be delivered to Mr. Mattis.
Mr. Minter said that based on that report, “We wanted to move as quickly as possible to nip that in the bud.” The lawsuit’s complaint stated that “upon information and belief, the White House turned that decision into official guidance, approved by the White House Counsel’s Office, to be communicated to the Department of Defense.”
Still, as of Wednesday, the White House had yet to send any specific policy directive to the Pentagon, said Lt. Col. Paul Haverstick, a military spokesman. He said General Dunford’s statement from two weeks ago remained in effect.
“There is no change,” he said. “We are still waiting for more guidance from the White House.”
The lawsuit complaint argued that banning transgender people from serving in the military would be unconstitutional discrimination, violating their rights to equal protection and due process. It also argued that the Pentagon could not end people’s military careers for coming out openly as transgender because they did so in relying on the Pentagon itself saying they would be permitted to serve.
Colonel Haverstick said the military was “aware of the lawsuit; however, we are not able to comment due to the pending litigation.”
Other rights groups preparing similar legal challenges said on Wednesday that they were still holding off. Among them were both Outserve and Lambda, which have said they were recruiting plaintiffs for a joint lawsuit when the matter is ripe, a legal term meaning the facts of a case have developed enough for a decision.
“We have not yet filed suit, although we stand ready to do so,” Jon Davidson, the Lambda legal director, said on Wednesday. “We have been awaiting confirmation that the White House has transmitted a final guidance, directive or other instructions to the Department of Defense, which, to the best of our knowledge, has not yet occurred.”
James D. Esseks, director of the American Civil Liberties Union’s Lesbian Gay Bisexual Transgender & HIV Project, said his group was also holding back, but noted that it has sent a letter to the White House asking it to preserve all documents related to the matter in anticipation of future litigation.
Even if the administration has not yet transformed Mr. Trump’s Twitter announcement into policy, it remained possible that it will do so by the time a judge has to decide whether the new lawsuit is ripe for adjudication or should be dismissed, experts said.
Regardless, Mr. Minter expressed confidence that the suit had not been filed too quickly. He noted that defending against the case would force the White House to talk about the status of plans to reinstate the ban, and he argued that there was “no downside” to a strategy of moving ahead now.
“I don’t think we will get dismissed on ripeness because people are being harmed now,” he said. “But if we do, we will be right back as soon as there is any additional movement.”