Do you really think the threat that “JD Vance might be unhappy with you, and would direct the literally tens of people who like him to vote against you in primaries” would keep the Republicans in congress under control? Trump’s whole thing is his weaponisation of a cult of personality. Vance doesn’t have a personality at all (and I’d assume he was chosen for that reason, Trump not wanting the competition.) He’d be dead in the water from day one.