Donald Trump is the first U.S. President to be on the record as having anti-vaccination attitudes. Given his enormous reach and influence, it is worthwhile examining the extent to which allegiance to Trump is associated with the public's perceptions of vaccine safety and efficacy. In both Study 1 (N = 518) and Study 2 (N = 316), Trump voters were significantly more concerned about vaccines than other Americans. This tendency was reduced to non-significance after controlling for conspiracist ideation (i.e., general willingness to believe conspiracy theories) and, to a lesser degree, political conservatism. In Study 2, participants were later exposed to real Trump tweets that either focused on his anti-vaccination views, or focused on golf (the control condition). Compared to when the same respondents were sampled a week earlier, there was a significant increase in vaccine concern, but only among Trump voters who were exposed to the anti-vaccination tweets. The effects were exclusively negative: there was no evidence that anti-vaccination Trump tweets polarized liberal voters into becoming more pro-vaccination. In line with the social identity model of leadership, Study 2 indicates that some leaders do not simply represent the attitudes and opinions of the group, but can also change group members' opinions.