McCain is intensely jealous because he thinks himself of as a war hero and lost the presidential election to a Muslim, while a man who never served in military easily beat the smartest woman candidate who was leading in every poll.
Not to mention the insults Trump threw at McCain this last election cycle.
I’m not sure whether it’s jealousy or resentment, but either way, McCain is completely and irretrievably around the bend over Trump. Plus, McCain’s secondary claim to fame is his alleged ability to work with Democrats (more precisely, his unceasing willingness to capitulate to them) so under these conditions, he can fight Trump all the way on every topic, act like a True Democrat, and yeah, there’s the war hero thing (that no Dem is) that’s always in the background. So he is so very, very special in his McCain-ness and so deserving of the attention showered upon him. Lately, I even notice a smallish gap between McCain and Linda Graham, his erstwhile love interest.