Most people forget that Trump hated Reagan, and said Oprah Winfrey would be the ideal running mate. Most of his donations went to democrats. At best, Donald has always been a part of the same Rockefeller wing that taxed & spent New York into oblivion.
When Trump first declared, I thought the exact same thing, and figured he might be the best the Dems could hope for from a nominal Republican. And I still think it might have turned out that way
if they hadn't gone after him so hard and so personally, and kept attacking him as soon as the morning after the election. I think Schumer actually knew that, and tried to meet with Trump early on. The problem was the left in his own party went insane over him meeting with Trump, and sent a clear signal that they wouldn't tolerate any Democrat working with Trump on
anything.
By default, that meant conservatives were left as Trump's only potential allies, so he went all-in with them from then on forward. And since he's a guy for whom
everything - including policy - is driven by personal relationships and how much others like
him, he's become more and more isolated. He gives the people who like him exactly what they want, which makes them like him more. And if you oppose him on anything, he takes that personally and starts opposing you on everything else. It's systemic polarization between Trumpers and everyone else at this point.