It's not _solely_ a Trump thing, but he gave RFK an enormous platform and has himself been espousing demonstrably untrue things about vaccines and vaccination schedules. This very week, in fact. [1]
If you don't see this as an enormous amplification, I don't think you're operating in good faith.
1. https://www.nytimes.com/2026/08/10/well/trump-vaccines-fact-...