Cults are hard to defy.
Like every other Congresscritter, Cuellar needs plum committee assignments producing inside information he can then trade on, to make money to pay his legal bills, and then, get rich.
For Cuellar, it was a cold calculation as to which party affiliation would allow him to conduct this grift most quietly and effectively. Nothing personal directed at PDJT.
Could he win as a D and then flip in office to R?