Most LGBT-rights activists never believed Donald Trump’s campaign promises to be their friend. With his move to ban transgender people from military service, on top of other actions and appointments, they now see him as openly hostile. Leaders of major advocacy groups depicted Trump’s pronouncement on Twitter as an appeal to the portion of his conservative base that resents the recent civil-rights gains by the LGBT community. Transgender service members have been able to serve openly since last year, when the administration of President Barack Obama made that possible. Trump’s vow to end that policy is the latest, and perhaps the most stinging, of a string of actions and appointments since his election that have dismayed supporters of LGBT rights.