It's not a permanent departure, but a concrete step towards the choice of banning transgender people from the US military, where they had found a place thanks to a provision of Barack Obama which also allowed the payment of medical expenses for the transition by the army. The Supreme Court, which is the most important legal body in the USA, voted in favor of the entry into force of the restrictions on the presence of transgender people in the army desired by the president Donald Trump in July of 2017.
The provision therefore comes into force pending the sentences of the courts to which the military has appealed. According to data from Human Right Campain there would be 15 thousand those in actual service and over 143 thousand veterans.

Human Rights Campaign

The #TransMilitaryBan prevents qualified transgender troops from openly serving their country. It’s discriminatory and unconstitutional. With as many as 15,000 trans service members and their families now at risk, there’s no time to waste. #ProtectTransTroops

Persons who have undertaken and completed gender transition are not eligible to join the U.S. military.. They will be able to stay in service how many already are and have entered declaring the gender they feel they belong to, even if different from that of birth. Those who do so by declaring their biological sex will be able to enter.
They voted in favor of the restrictions 5 of the 9 Supreme Court judges, opposite i 4 progressive in orientation.
Trump had launched the trying with a tweet in July of 2017. “Our military must focus on decisive and overwhelming victory and cannot be burdened by the tremendous medical costs and disruptions that being transgender would entail.”. The medical expenses brought as an excuse are however, according to the Cnn, very limited. The army spends 5 times more in Viagra according to Military Times.
Instead, there is the will told a few months ago by New York Times to insert a rule according to which a person's gender can only be determined by «clear and objective biological elements» that is, from the genitals at birth. A rule like this would deny many of the rights acquired in recent years by Transgender people, effectively denying their existence. The right to choose the bathroom for transgender children at school has already been cancelled.

Playboy

Despite some 134,000 transgender veterans and 15,000 trans soldiers actively serving in the U.S. military, the Supreme Court has decided to allow Trump’s #TransMilitaryBan to go into effect. To those serving the United States proudly, we support you. https://bit.ly/2FPpInw

There are many tweets against this decision from well-known people and much of Hollywood. There is also that of Playboy who chose a transgender playmate already in 2017.