AP PHOTO President Donald Trump turns to walk back to the Oval Office after speaking in the Rose Garden of the White House in Washington, Wednesday, during an American Legion Boys Nation and the American Legion Auxiliary Girls Nation event.

WASHINGTON — President Donald Trump abruptly declared a ban Wednesday on transgender troops serving anywhere in the U.S. military, catching the Pentagon flat-footed and unable to explain what it called Trump’s “guidance.” His proclamation, on Twitter rather than any formal announcement, drew bipartisan denunciations and threw currently serving transgender soldiers into limbo.

“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,” the commander in chief tweeted.

Trump wrote that he had consulted with “my generals and military experts,” but he did not mention Defense Secretary Jim Mattis, the retired Marine general who less than one month ago told the military service chiefs to spend another six months weighing the costs and benefits of allowing transgender individuals to enlist. At the time, Mattis said this “does not presuppose the outcome of the review,” but Trump’s tweets appeared to have done just that.

The Pentagon has refused to release any data on the number of transgender people currently serving. A Rand Corp. study has estimated the number at between 1,320 and 6,630 out of 1.3 million active-duty troops.

Criticism for Trump’s action was immediate and strong from both political parties.

His action is “harmful, misguided and weakens, not strengthens our military,” said Democratic Sen. Kirsten Gillibrand of New York.

John McCain, the Arizona Republican and Vietnam War hero, said Trump was simply wrong.

“Any American who meets current medical and readiness standards should be allowed to continue serving,” he said. “There is no reason to force service members who are able to fight, train and deploy to leave the military — regardless of their gender identity.”

Rep. Duncan Hunter, a member of the House Armed Services Committee, said, “The president’s decision was the absolute right decision. … It’s about time that a decision is made to restore the warrior culture and allow the U.S. military to get back to business.”

Transgender people already in uniform were concerned about what comes next.

“Everybody is hurt, everybody is scared,” said Rudy Akbarian, 26, who is in the military but did not want to identify his branch.

Akbarian, who said his chain of command was supportive as he transitioned from female to male, said his time to re-enlist is coming up and he might stay to ensure there is a strong voice for transgender troops like himself.

“I’m going to remain hopeful,” he said. “America is really progressive and definitely smart, and there are a lot of transgender members serving in critical roles.”

Shane Ortega, a 30-year-old retired staff sergeant in Los Angeles, said he’s concerned more for civilians than transgender troops.

Ortega, who transitioned to male while serving in the Army and served combat tours in Iraq and Afghanistan, said, “When Donald Trump attacks what America calls its heroes or its warrior class, it means it’s only a matter of time before he starts attacking and disassembling the American public, and that’s what I have the most fear of.”

Hours after Trump’s tweets, Defense Secretary Mattis, who has been on vacation this week, was publicly silent and the Pentagon referred all questions to the White House.

Navy Capt. Jeff Davis, a Pentagon spokesman, said the Pentagon was working with the White House to “address the new guidance” from Trump. That suggested there is not yet any new written policy or executive order.

Trump’s sudden declaration appears to halt a decades-long trend toward inclusive policies on military service, including the repeal in 2010 of a ban on gays serving openly. President Bill Clinton in 1993 began the push to allow gays to serve. In December 2015, President Barack Obama’s Pentagon chief, Ash Carter, announced that all military positions would be open to women. Liberalizing policy on transgender troops was the next step.