It's not just that he promoted anti-trans rhetoric. He made clear promises. Not just his off the cuff, stream of consciousness stuff, but actual position statements still up on his campaign site.
The gist of it is a culmination of all the worst anti-trans laws so far. Banning trans health care for all ages, prosecuting providers and prohibiting legal transition - including reverting ID's & BC's regardless of how long ago someone had them changed.
https://www.reddit.com/r/transgender/comments/1gmbz28/comment/lw1eomb/