https://news.yahoo.com/trump-dismisses-covid-19-booster-184022005.html
It sounds like Trump is now beginning to publicly cast some doubt on the vaccines. He's starting cautiously, by questioning the booster shots, but I suspect (hope) that he will be slowly ramping up the questioning and criticism going forward, from here on out.
Again, this was always about the existence of a vaccine. The existence of a vaccine destroys their argument for lockdowns which would ultimately destroy America if they were allowed to go on indefinitely. Now that a vaccine exists, there is no need to support boosters. The sheep can do what they want, but boosters aren't necessary to destroy the lockdown narrative, only the original vaccine. And the more they admit the original vaccine doesn't work, or provides only limited protection which quickly wears off, the more they risk the sheep waking up.