I don’t think he really has an iron grip. I do think that a lot of conservatives have become disenchanted with Trump. It was fine when he was giving positive momentum to the party. But lately he’s been a drag.
He never had an Iron grip. First Paul Ryan and Mitch McConnell allowed the Russia gate Hoax to foster when they were in charge of the house and senate during his first two years, as a way of stopping him from not doing “business as usual” in DC. Then McConnell continues to stab him in the back, because it’s better to be the literal #2 he is than have to actually do things openly in the Senate. Better a backroom deal with Schumer than a deal with the american people. He gives crap a bad name.