In laying out his reasons for moving on Wednesday to ban transgender people from serving in the U.S. military, President Donald Trump cited the "tremendous medical costs" associated with the policy.

His claim raises several immediate questions, such as exactly how much the Department of Defense spends on providing health care for transgender service members, as well as whether there are enough transgender people in the armed forces to move the needle on the department's annual $6 billion in health care spending on active-duty forces.

....victory and cannot be burdened with the tremendous medical costs and disruption that transgender in the military would entail. Thank you — Donald J. Trump (@realDonaldTrump) July 26, 2017

The answer? President Trump's assertion that permitting transgender people in the armed services entails major health care costs appears to be overblown, based on estimates from the think tank RAND, which was asked by the Department of Defense to study the issue last year. Health care costs for treating active members who want to transition to another gender would increase by between $2.4 million to $8.4 million annually, RAND found. That translates to 0.04 percent to 0.13 percent of the agency's annual spending on health care.

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"Our study found that the number of U.S. transgender service members who are likely to seek transition-related care is so small that a change in policy will likely have a marginal impact on health care costs and the readiness of the force," the Rand researchers wrote.

Likewise, a 2015 study in the New England Journal of Medicine concluded that the health care costs related to transition for transgender service members "is too low to warrant consideration in the current policy debate." Its author estimated the costs at $5.6 million annually, or "little more than a rounding error."

Mr. Trump's announcement reverses an Obama-era military policy that began last year under which transgender service members may openly serve in the military. Since that policy was implemented, transgender troops have been able to receive medical care and start changing their gender identification in the Pentagon's personnel system.

When former Secretary of Defense Ash Carter announced the transgender service policies in 2016, he cited RAND's estimate that about 2,500 people, out of 1.3 million active-duty service members, are transgender.

"The medical treatment that service members who are currently transgender requires fairly straightforward, well-understood," Carter said at the time in a press briefing to discuss the policy. RAND was "able to make those estimates. And that was, as they said, minimal."

Some military personnel are already in the process of changing gender, or have been formally approved to change gender. The numbers are small, however, with the Associated Press noting it currently stands at about 250 service members.

NEW: Former Defense Secretary Ash Carter responds to President Trump's Transgender Ban pic.twitter.com/p8jY1FfXDZ — CBS Evening News (@CBSEveningNews) July 26, 2017

Carter spoke out on Wednesday against President Trump's transgender ban in a statement to CBS Evening News. " To choose service members on other grounds than military qualifications is social policy and has no place in the military," he said. "There are already transgender individuals who are serving capably and honorably."

Some conservatives said they supported President Trump's ban. Rep. Vicky Hartzler, R-Missouri said Wednesday in a statement that "sex-change surgeries" would "cost more than a billion dollars over the next ten years." She didn't cite a source for her estimate.

Even if the military spent at the top end of the estimated range for health care on transgender service members -- $8.4 million per year -- it would reportedly represent a fraction of what it spends on Viagra. The Department of Defense spent $41.6 million in 2014 on the erectile-dysfunction drug, or about five times what transgender service members would cost, according to an estimate from the Military Times.