The Republicans act as though Trump will remain a powerful force in the party after he leaves office. They are afraid he will oppose their re-election in a couple of years if they go against him.
I understand that he has raised big money since leaving office, and could use it against those he perceives as enemies. But I think he will use that money differently (since it went to the kind of PAC that allows him to spend it as he wishes).
I think he will use that money for his own benefit. He has huge debts coming due soon after he leaves office, and he also has a host of legal problems that will pop up as soon as he's no longer in office. He's going to use that money to offset those problems.
Maybe I'm wrong, but I think his power is going to fade fast after he is no longer president. And the same goes for his kids. Their only power came from being his children while he was president, and it will fade even faster than his will.