Since last year, thanks to the work of Obama's administration and Secretary of Defense Ash Carter, transgender people were able to serve openly in the US military, with access to insurance coverage for transition-related medical procedures.
Trans people had to be able to join the army as of July 1, 2017, but a few weeks ago, the new defense secretary James Mattis delayed the enrollment of trans recruits by six months.
Today, Trump decided to officially ban trans people from serving.
This will lead to preventing new transgender recruits from joining the US military. This will also lead to the discharge of openly trans people who now serve openly in the US military. Finally, it will strengthen the anti-trans feeling that is developing in the United States.