Turn it around on them. Make them show you their genitals before they go in the bathroom. Then have them arrested for showing you their genitals.
Yes, I see no ways that a trans person asking to see peoples' genitals in a public restroom in a jurisdiction that is hostile to trans people could backfire.
That doesn't sound like the Democrats I know! They would post a comment on social media about how sad they are about it and then say "vote blue, no matter who!" before defending some softer form of transphobia as a middle ground.