I don't see why Trump wouldn't have that constituency still available to him. Not only is he the leading candidate by a country mile to win the Republican nomination, he has also become the north star of his party, and every politician dovetails their efforts into appearing to be with him and on his team.
But it's also a symbiotic relationship. It's not only that Trump's blessing gives those lesser pols legitimacy—it's also that their very fealty gives Trump his legitimacy as well. Everyone comes of as being on the same page, and constituents respond positively to that kind of unity at the top of their preferred structure.
I would bet that if R politicians could manage to peel off from Trump en masse, preferably maintaining the Trumpy populist appeal, Trump himself would be finished. That's a tricky task, because as we have seen recently from DeSantis, nobody can Trump like Trump. It's not just his cruel policies or his middle-school-level nastiness—it's also the Trump charm, such as it is. No one has been able to come close to replicating whatever that thing Trump has that charms his fans so.
As a result, no one lesser light can effectively be the one to lead that defection, and every one who has tried over the past several years has failed, for reasons. That's why Republicans keep rooting for someone else to magically break Trump's spell, finally, because they can't do it themselves. They know all that red meat is bad for them, but they just can't stop eating it. In order to survive, they need someone to force them to stop. Who going to be the one to do that?