"They have not only nearly destroyed their own party"
The current intra-Democratic frustrations don't really have that much to do with nailing down their stance on the gender identity movement (though it could be a factor down the line), but have more to do with the old guard and young progressives disagreeing with the direction the party should take.
"they have foisted Trump on the American people"
It's important to keep in mind that the portion of US voters concerned about the clash of gender identities and material reality (including some gender-critical feminists) had a chance to attempt to untangle this mess via the legal system, public pressure campaigns, etc., a good while before the presidential election campaigns really kicked into gear and Trump seized the narrative.
It's not as if they had no choice but to helplessly stand by and watch right-wing politicians and commentators control the narrative for their own private gain.
No direct equivalent of the Equality Act exists in US federal law, so concerned people could not have sought legal clarity the exact same way UK feminists have sought it via the FWS v The Scottish Ministers case.
But it's telling that despite the sociopolitical and legal differences there were still legal avenues left unexplored in the US before the transgender issues became politically salient, and yet there are some who appear to essentially espouse "well, I haven't tried much but I'm out of all ideas".