AFTER BEING caught by surprise by a series of tweets in July 2017 from then-President Donald Trump ordering a ban on transgender troops, the leadership of the Pentagon scrambled to concoct a plan to do the president’s bidding. It was a stark and sad contrast to the rigorous, year-long study undertaken by the Pentagon during the Obama administration that had opened the way for transgender people to openly serve in all branches of the service. President Biden’s decision to lift the Trump administration’s ban on transgender troops marks a welcome return to policy based not on political whim or expediency but on fact and reason.

Mr. Biden said during his campaign for president that putting a quick end to the transgender ban was “not just the right thing to do, but it’s in our national interest.” He lived up to that promise, signing an executive order on Monday that restores the protections put in place by the Obama administration in 2016 that had lifted the ban against transgender people serving in the armed services. “We don’t want barriers unrelated to a person’s qualifications to serve,” said then-Defense Secretary Ash Carter, “preventing us from recruiting or retaining the soldier, sailor, airman or Marine who can best accomplish the mission.”

Mr. Trump’s capricious tweet announcement upended the premise that military service should depend on capability, not gender identity or sexual orientation. That leaders of the Army, Navy and Marine Corps had told Congress that they were not aware of any negative effects from transgender personnel serving mattered not at all to Mr. Trump. Nor did the fact that a majority of Americans supported transgender people serving in the military. For the first time in American history, a minority group that had been allowed in the military was subsequently banned, and for no good reason.

A study last November concluded that the ban against transgender troops had eroded the military’s ability to fight and win wars by limiting its recruiting pool and lowering morale among transgender people who had been grandfathered into service. The regulations implemented in 2019 prohibited anyone with gender dysphoria from enlisting but allowed transgender service members who were serving before then to remain. Contrary to Mr. Trump’s protestations that barring transgender people from service would improve readiness and strengthen unit cohesion, the study by three former military surgeons general and the Palm Center, a research institute that studies LGBTQ personnel issues in the military, said the opposite had occurred. “The transgender ban has harmed military readiness across the board. That’s what happens when the military needlessly discriminates against people who are qualified to serve,” said Alan M. Steinman, a former U.S. Coast Guard director of health and safety and retired rear admiral of the U.S. Public Health Service Commissioned Corps.

Because the Obama administration had developed policies for how the different military branches would implement changes in recruiting and retainment, Mr. Biden’s executive order can have an immediate beneficial effect. What a relief to see decision-making based on evidence, not prejudice.

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