The Supreme Court announced on Tuesday in a 5-4 decision that they would allow the transgender military ban to go into effect while the lower courts continued to hammer out the issue. To be clear, they did not rule on the merits of the case (whether the president can and should transgender people from serving in the military) they just said that the ban could continue for now.
In July 2017, President Trump announced a ban on transgender people being able to serve in the military. Then-Secretary of Defense Jim Mattis put in place a more detailed policy. When the ban was put on hold by lower courts, the Trump administration went right to the Supreme Court and asked for the ban to go into effect while the challenges moved forward, claiming it was an issue of national security. Today, four of the more liberal Judges (Ginsburg, Sotomayor, Kagan, and Breyer) said they would not have allowed the ban to continue. However, they were overruled by the five other justices, and the ban will continue to work its way through the lower courts.