Romney hates Trump due to pure and extreme jealousy. I read many reports that he was shocked and very angry when he lost to Obama. And then to see Trump do SO well with voters in 2016; well, I think he still can't get over it. Trump was loved then, and is adored now. His support probably doubled in 4 years. No voter ever loved, or even liked Romney. They just tolerated him and/or wanted Obama out.