I grew up in NY and followed the man from the 80's on. Dump is an idiot and a life long Dem till recent years. But mostly he is an opportunist and a whore. Seems Republicans admire that nowadays. Who knew.Trump was a Republican. Watch his old clips when he was younger. He said he was a Republican because he believed the same values (most of them).
The reason he went to Democrats after that is probably because he wanted to run for president. He went in to learn about how corrupted the Democrats are and the establishment in general. As the saying goes, "know your enemy and you will win the war." Trump is a very smart and calculated man. The Dems establishment didn't see that coming.
Bloomberg did the same thing. He was a life long Dem that wanted to run for mayor of NY. The Democratic political machine wouldn't give him the time of day. So he said screw you and ran as a Republican. Won not once, twice but three times. Difference with him is he actually accomplished something. Dump other than stacking SCOTUS with more Conservatives has done shit.