Believe it truly literally? No

It’s a concept known as Kayfabe. A special kind of pretending, where both performer and audience act as if something is real, when both know it isn’t. It started with American professional wrestling. Wrestlers would greet fans after the show and sign autographs as their characters, not as themselves.

So no, even his MAGA supporters don’t literally believe he’ll give them $5k, they just accept is as a promise that he and the republican will do good things for them generally. They like the sound of it, even though they know it’s not real.