This seems like a bizarre retcon. No only did Trump fund "Operation Warp Speed" but he still (occasionally) expresses pride at funding the vaccine research. This is not "casting doubt on vaccination". I think the US right was generally doubtful of vaccination, but I'm fuzzy about whether this started before or after the vaccine mandates. Certainly I remember it being more of a phenomenon once Biden took office - perhaps as knee jerk opposition to a Democrat president.