A California congressman fired back at President Donald Trump’s Twitter announcement barring transgender service members, saying the decision will affect thousands of people.

Trump announced the decision in a series of tweets on July 26, 2017.

"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."

U.S. Rep. Ted Lieu, D-Calif., later told CNN anchors John Berman and Poppy Harlow that Trump’s policy will force good people into hiding and prevent them from serving their country.

"You've got thousands of people serving in the military who are transgender and they're doing a fantastic job," said Lieu, who holds the rank of colonel in the Air Force Reserves.

Lieu repeated the sentiment in a statement he also echoed on his Facebook page and Twitter account.

We wondered how many service members identified as transgender, something the U.S. Defense Department didn’t disclose to us. But a couple of estimates show that there are likely thousands of transgender soldiers, sailors and airmen.

Estimates but no complete data

Trump’s announcement reversed a policy announced under President Barack Obama in June 2016 that ended the service ban on transgender Americans, which had stayed in place even after Congress repealed the so-called Don’t Ask, Don’t Tell law for gays and lesbians in December 2010.

Transgender soldiers, airmen and sailors would have faced being medically discharged for disclosing that information, but Obama’s policy allowed those service members to serve openly if they chose. His administration gave the military until July 1, 2017, to fully implement the rule.

On June 30, Defense Secretary James Mattis delayed implementation by six months, before Trump appeared to revoke the rule entirely via Twitter.

As many as 250 service members have asked to formally change their preferred genders, or have already been approved, the Associated Press has reported.

The Defense Department would not elaborate on Trump’s announcement, including how many transgender people served in the military. Reports have said the Pentagon does not keep track of transgender personnel.

Instead they sent us to the military’s transgender policy web page, which as of this writing had not yet been updated. A Defense Department spokesman said the policy would be revised "in the near future," with White House input. A Trump spokesman did not answer our attempts to contact him.

Lieu spokesman Jack d’Annabale said the congressman got his estimate from a May 2014 brief by researchers at UCLA’s Williams Institute on Sexual Orientation and Gender Identity Law and Public Policy.

They used responses to the National Transgender Discrimination Survey, sent to respondents by the National Gay and Lesbian Task Force and the National Center for Transgender Equality. The definition of transgender included "those whose gender identity or expression differs from those traditionally associated with their assigned sex at birth," according to the study.

Extrapolating that 0.3 percent of the population identified as transgender, UCLA’s researchers estimated that there were "approximately 15,500 transgender individuals are serving on active duty or in the Guard or Reserve forces." It also said that about 134,400 transgender people were veterans or retired.

Another study published in the New England Journal of Medicine in September 2015 used data from the UCLA brief and other sources to determine that 12,800 service member would be eligible for transgender health care. The study suggested of those, 188 would use benefits for transition services, at a cost of $4.2 million to $5.6 million.

More recently, the Pentagon commissioned a June 2016 RAND Corporation report studying the effects of integrating transgender service members. (CNN’s Berman actually mentioned this one during Lieu’s interview.)

The think tank estimated that there were between 1,320 and 6,630 active duty transgender personnel, and between 830 and 4,160 in the reserves. The midrange estimates were for 2,450 active duty and 1,510 reserve duty service members.

As a side note to Trump’s concern over costs: Only a fraction of active duty transgender service members were likely to seek medical treatment, the study said, resulting in a high-end estimate of an $8.4 million increase in health care costs, or 0.13 percent.

The RAND study used the National Transgender Discrimination Survey and other surveys, including private insurance data. RAND started with a lower population prevalence than UCLA did — 0.19 percent instead of 0.3 percent — accounting for the lower figure.

If we combine the top RAND estimates for active duty and reserves, between 2,150 and 10,790 active duty and reserve service members may identify as transgender.

Defense Department projections for the 2017 fiscal year were for 1.28 million active duty personnel and a little more than 800,000 in the reserves.

Our ruling

Lieu said, "You've got thousands of people serving in the military who are transgender and they're doing a fantastic job."

There are no solid numbers from the Defense Department, but two sources have provided recent estimates extrapolated from survey and insurance data. One 2014 UCLA brief estimated as many as 15,500 active duty and reserve service members may identify as transgender. A 2016 RAND Corp. study commissioned by the Pentagon suggested between 2,150 and 10,790 active and reserve duty troops.

While both estimates said there are likely thousands of transgender people in the military, those are still estimates. Lieu should note that in his talking point.

We rate the statement Mostly True.