I consider myself to be a Reagan Republican. There is no principled way to support or justify Trump's position here. I hope that this is just Trump being an attention whore, and he eventually returns to Ukraine after Zelenskyy says that he is "sorry". But if the U.S. turns its back on Ukraine and supports Russia, that is different than America-first isolationism. That would be a betrayal of everything that the U.S. has stood for internationally since 1941.
Democracy is qualitatively different than tyranny. One should be supported, the other should be opposed.