Trump didn't change the party, trump tailored his message to appeal to those who didn't identify with rank and file republicans. Other republicans saw that trumpism was a winning message and they pulled the party to where he was, all for power. The party leaders, McCarthy, Graham, McConnell all career politicians, all formally bush republicans, moved themselves and the party to maga. They did stupid crap like let Ronna McDaniel chair the party. They were both scared of trump and envious of his ability to bring others into the party.