I still believe that they're mad as fuck because the elites truly thought he was "one of them" by allowing him into their circles. They
all used to worship and kiss the ground he walked on, and they all cracked jokes and stuff about their debauchery lifestyles. Then he ran on a Republican ticket and they freaked out, even though he was a known flip-flopper about his political affiliations since the '80s. But another thing that I think really gets under their skin is that Trump knows all of their dirty secrets, he has connections everywhere, and he's more than willing to use it against them. They've been struggling to find a way to get
something to stick to Trump in return as a "Gotcha, bitch!", but he's shrugged it all off. Meanwhile, their skeletons have been falling out one by one.
But associating himself with the commoners practically since the beginning of his career I'm sure was always something they sneered at behind his back. They're just not bothering to hide it anymore.