In mid-February, on the day that the Senate confirmed Robert F. Kennedy, Jr., as Secretary of Health and Human Services, Del Bigtree, an anti-vaccine activist who had served as the communications director of Kennedy's Presidential campaign, hosted an event at the National Press Club, in Washington, D.C. Bigtree was now the C.E.O. of the advocacy group MAHA Action, and the National Press Club event, where members of the media gathered in a modest room with a small stage, was a celebration of sorts.