It's not about winning.
All that matters to most is that the other side loses.
I'm tired of hearing this knee-jerk Both Sides fallacy. And it's just that: a fallacy.
Republican and Democratic party members have very different mindsets and goals. For all our faults on the Dem side, we don't respond to authoritarian strong men, whereas Republicans do. Trump -- who has never had any specific party affiliation -- is running as a Republican because those voters respond to his whiny, petulant Aggrieved White Man persona, whereas Democrats largely do not. If party affiliation was simply a neutral choice, a flip of the coin, then Trump could have run as a Democrat and done as well, but he didn't. The closest candidate to Trump on the Dem party side was Bloomberg and he got nowhere with his presidential bid. Because Democrats don't like that shit.
If by some ugly twist of fate Trump had run as the Democratic nominee, I'd hold my nose and vote for someone like Romney or Kasich, even -- God help me -- Ted Cruz. Because policy, competence and character matter to me, and Trump has always been a delusional grifter of jaw-dropping incompetence. He's completely unfit for office, regardless of party affiliation. I will vote country over party every time, but as has become glaringly obvious, most Republicans will not.