Cassidy took that chance on Wednesday, using his position inside Senate committees to probe Kennedy’s approach to public health at a moment when vaccine policy has become a flashpoint inside U.S. politics. In two hearings that combined oversight with campaign stakes, Cassidy questioned the health secretary on affordability and fraud, and on the risk of outbreaks of vaccine-preventable diseases, including measles.
The senator’s performance underscored what the hearings meant for him personally. Cassidy, who chairs a Senate committee overseeing part of Kennedy’s department and sits on another, came to the exchanges with medical experience and a history of clashing with Kennedy’s vaccine agenda, even as he voted for Kennedy’s confirmation last year after securing commitments tied to vaccine approval and safety monitoring and support for the childhood vaccine schedule.
During the questioning, Cassidy said he is a doctor who has seen people die from vaccine-preventable diseases, and he argued that when outbreaks reach “numbering in the thousands” and deaths occur again—“particularly children”—it is more than tragic. He also described declining vaccine confidence in the U.S. over the past year, and asked how Kennedy would address expected outbreaks of vaccine-preventable diseases with the upcoming World Cup and America 250 events.
Cassidy’s opponents and political allies watched how he framed those risks. Claire Leavitt, an assistant professor at Smith College who studies congressional oversight, said Cassidy’s actions in the hearings reflected “any sort of resistance to RFK” and could carry an electoral price. Mary-Patricia Wray, a Louisiana political consultant, said Cassidy’s approach functioned like a “polite ‘I told you so,’” while Cassidy reinforced “real-world consequences” of declining vaccine confidence and signaled that the administration’s posture was moving closer to where he has been as a physician.
The hearings also highlighted the political tightrope Cassidy has walked since he backed Kennedy’s nomination. Cassidy’s medical background includes advocating for babies to receive hepatitis B vaccines shortly after birth, which he said could have prevented disease in his patients. When Trump nominated Kennedy—an anti-vaccine activist—Cassidy supported the nomination only after seeking commitments that Kennedy would work within the existing vaccine approval and safety monitoring system and back the childhood vaccine schedule.
Cassidy’s support for Kennedy did not ease the political conflict that followed. Trump endorsed U.S. Rep. Julia Letlow, one of Cassidy’s two opponents in the next-month Louisiana primary, in an unusual move aimed at ousting a sitting senator from his own party. Cassidy also faces pressure from the “Make America Healthy Again” movement, which includes anti-vaccine activists, and related political activity—such as the MAHA PAC’s pledge of $1 million to Letlow’s campaign—while some critics have questioned whether MAHA’s support includes retaliation for Cassidy’s vaccine-related criticism.
Cassidy had previously described his relationship to the movement in ways that underscored both overlap and disagreement. He told reporters earlier this month that he is the reason Robert F. Kennedy is now secretary of HHS, and he said Kennedy “would not have gotten there otherwise.” Cassidy said he has “strongly supported” MAHA’s agenda, especially its focus on fighting ultraprocessed foods, while acknowledging that he and MAHA have “disagreed on vaccines,” adding that he and his critics “seen, frankly,” that he is right when pointing to recent measles-related deaths of children who were not vaccinated.
In Wednesday’s hearings, Cassidy also sought to demonstrate willingness to push back even from the political right. Wray said the senator asked Kennedy why HHS has not reinstated an in-person dispensing requirement for chemical abortion drugs, and she said the line of questioning reflected an attempt to court non-MAHA Republican voters who want the administration to do more on priorities.
How Cassidy handles the hearings may also shape what comes next for Senate oversight of HHS. Leavitt said seniority typically determines who chairs Senate committees, and she warned that in a hyperpartisan Congress another Republican may be less willing than Cassidy to check Kennedy’s power. Dorit Reiss, a vaccine law expert, said she wished Cassidy had held more hearings or introduced legislation to rein in Kennedy, and she also argued that Cassidy bears blame for allowing Kennedy to bring unfounded vaccine fears into government in the first place.
The hearings took place as vaccine policy continued to intersect with wider political messaging, including questions about who is seen as trusted to oversee public health institutions. Cassidy had earlier raised concerns in past hearings about Kennedy’s efforts to slash funding for mRNA vaccine development, questioned Kennedy’s attempt to replace members of a vaccine committee, and asked about concerns that Kennedy’s vaccine policy decisions could make it harder for Americans to get COVID-19 shots. Later in the year, Cassidy convened a hearing that included former CDC Director Susan Monarez, who was ousted after clashes over vaccine policy, and former CDC Chief Medical Officer Debra Houry, who resigned citing an erosion of science at the agency.
Asked about the approach that emerged from Wednesday’s Senate questioning, experts said the episode could affect Cassidy’s reelection prospects and set the tone for future congressional oversight. As the next-month primary approaches, the congressman’s medical and committee background are now inseparable from the political calculus of whether he can demonstrate both independence from Kennedy and alignment with the voters his opponents are trying to mobilize.