Trans rights are human rights, and how you treat anyone in your society is how you treat everyone. Democrats were scared in the '80s and '90s to support gay people for this exact reason, and instead of losing elections they started winning because people realize gay people are people. They lost elections because they weren’t brave enough to stand with the courage of their convictions, and in my opinion that’s what they deserved.
The current democratic party isn’t standing for trans rights any better than anyone else. Perhaps individual politicians are, but the party has a lot of de facto republicans in the ranks. So vote for them or not, they aren’t going to make things better for folks that are trans. They also aren’t ending wars, reducing military spending, helping vulnerable people seeking asylum, helping homeless people, providing free mental healthcare or national healthcare at all, and so on. Hell, they haven’t enshrined abortion rights into law in the past almost 50 years.
People vote for democrats because of tradition and lesser-of-the-evils reasons. That’s it. That’s a shitty place to be, and should embarrass us the voters as well as the party.