It was picked as a wedge issue but the Republicans chose very wisely, as the Democrats' incessant pushing of trans issues without any consideration towards the negative impact upon women and girls was unpopular even amongst many traditionally left-leaning voters.
If you mean that the Democrats' policy of supporting transgender rights through legislation was hard to defend (not from a scientific or medical standpoint, but from a populist, political one) and Trump effectively attacked it then yes you're right.
If you mean that the messaging on trans rights alienated swing voters then I think it's probably true, but moderates and swing voters do support general anti-discrimination laws but are wary of policies on sports participation and youth medical care.
If you mean that it was the centerpiece of their identity and everything that were campaigning for, and their pivotal, most important issue, then I don't think that's accurate.
But they did deliberately elevate transgender rights as a moral and civil rights issue. This was a trade off (energize progressives, lose some moderates). Conservatives effectively focused on targeted attacks (bathrooms, sports).
I think that maybe the gamble didn't pay off. The messaging should have probably been about protecting from discrimination, and debate should be focused on attacking republican establishment for being aggressive and hateful.
But really all of this doesn't matter. A better candidate, a white or latino strong charismatic man would have beaten Trump.
