On Wednesday, September 17, 2025, the U.S. Senate health committee will convene a high-stakes hearing that has Washington’s political and public health circles buzzing. At the center of the storm: Susan Monarez, the former director of the Centers for Disease Control and Prevention (CDC), who was pushed out of her role just weeks ago by Health Secretary Robert F. Kennedy Jr. Monarez’s testimony, called for by committee chair Senator Bill Cassidy of Louisiana, is poised to shine a harsh light on Kennedy’s controversial approach to vaccine policy and his management of the nation’s top health agency.
Monarez’s abrupt ouster in August 2025 followed a tense exchange with Kennedy. According to The New York Times, Monarez called Senator Cassidy to warn that she might not be around much longer, detailing that Kennedy had ordered her to fire top CDC officials and to accept vaccine recommendations from his own handpicked advisers—or resign. Within two days, the White House fired her. Monarez, for her part, has insisted she never refused to be “trustworthy,” as Kennedy claimed. Instead, she told the secretary, “if he believed he could not trust me, he could fire me.”
This episode is just one chapter in a saga that has put Senator Cassidy in a precarious position. Cassidy, a physician and longtime vaccine advocate, voted to confirm Kennedy as health secretary earlier this year, based on Kennedy’s personal promise to protect access to vaccinations and to maintain a close, collaborative relationship with the senator. But as Kennedy’s tenure unfolded, Cassidy’s faith has been sorely tested. He now finds himself caught between a restive Republican base at home—where he faces a tough primary challenge—and growing criticism from national public health leaders who once considered him an ally.
“Cassidy is a courageous person who, at the end of the day, concerns himself more about policy than politics,” Senator Thom Tillis of North Carolina told The New York Times. Yet Cassidy’s support for Kennedy, followed by his public waffling and eventual criticism, has left him “in big trouble” in Louisiana, according to Republican pollster John M. Couvillon. The state, which handed President Trump a decisive victory last year, is now the epicenter of a whooping cough outbreak that has claimed the lives of two infants—a crisis that only intensifies the scrutiny on both Cassidy and Kennedy’s public health decisions.
In recent months, Kennedy’s actions have repeatedly sparked outrage among vaccine advocates and lawmakers alike. In June, he fired all 17 members of the CDC’s Advisory Committee on Immunization Practices (ACIP), replacing them with individuals, some of whom are openly skeptical of vaccines. Cassidy, alarmed by the move, warned on social media, “Of course, now the fear is that the ACIP will be filled up with people who know nothing about vaccines except suspicion.” He later called for the panel’s meetings to be postponed, citing concerns that the new members “lack experience studying new technologies such as mRNA vaccines, and may even have a preconceived bias against them.” Nonetheless, the meetings proceeded as planned.
Matters escalated further when Kennedy canceled nearly $500 million in government grants for mRNA vaccine research—the very technology that underpinned the rapid development of Covid-19 vaccines. Cassidy described the decision as “unfortunate,” and at a contentious Senate Finance Committee hearing in early September, he accused Kennedy of making it harder for Americans to access coronavirus vaccines. “Effectively, we’re denying people vaccine,” Cassidy declared. Kennedy shot back, “You’re wrong.”
Beyond the policy disputes, the drama has exposed deep rifts within the Republican Party. Many prominent Republicans view Kennedy, a scion of a storied Democratic dynasty, as a liability for the MAGA movement and the broader GOP brand. Yet, as POLITICO reports, President Donald Trump has stood firmly by his health secretary—even as controversy swirls. “If you look at what’s going on in the world with health and look at this country also with regard to health, I like the fact that he’s different,” Trump said after a recent hearing involving Kennedy. Trump’s support is notable, given his reputation for quickly ousting high-profile appointees who fall out of favor. In Kennedy’s case, Trump appears to respect his independent political power and broad base of support, which overlaps but remains distinct from the MAGA faithful.
Trump’s public backing of Kennedy has even influenced his own rhetoric. In early September, Trump posted on Truth Social, pressing Covid vaccine makers for proof of efficacy and echoing some of Kennedy’s skepticism: “Many people think they are a miracle that saved Millions of lives. Others disagree! I want the answer, and I want it NOW.” This tolerance for Kennedy’s maverick style stands in stark contrast to Trump’s treatment of figures like Elon Musk, whom he expelled from government circles without hesitation when public sentiment turned sour.
Meanwhile, Cassidy’s efforts to assert oversight have grown more urgent. He has called for the indefinite postponement of CDC advisory committee meetings, citing “serious allegations” about the agenda, membership, and lack of scientific rigor. He’s also engaged in public disputes with other Republican doctors, including Senator Rand Paul of Kentucky, over routine vaccination policies. Paul opposes giving the hepatitis B vaccine to newborns, while Cassidy, a liver specialist, supports it, citing personal experience caring for an unvaccinated young woman who contracted the disease.
Public health leaders are watching closely. Dr. Georges Benjamin, executive director of the American Public Health Association, lamented that Kennedy’s “dysfunction, in many ways, undermines Cassidy’s credibility.” Dr. Celine Gounder, an infectious disease specialist and editor at large for public health at KFF Health News, observed that Cassidy’s confirmation vote for Kennedy “looks increasingly at odds” with his professed commitment to vaccine access. Dr. Paul Offit, a prominent vaccine advocate, went so far as to urge Cassidy in an open letter to call for Kennedy’s resignation, writing, “Senator Cassidy, it is not too late to do something about this.”
Back in Louisiana, the stakes are not just political—they’re personal. The state’s whooping cough outbreak has put Cassidy’s public health record under the microscope. On September 12, he posted a letter on social media pledging to work with Kennedy to address the crisis and publicly called on the health secretary to promote vaccination. A spokesperson for Kennedy responded that the department was “working closely with the State of Louisiana and its public health agency to monitor its pertussis caseload.”
As Monarez prepares to testify, alongside former CDC chief medical officer Dr. Debra Houry, who also resigned under Kennedy’s tenure, the Senate health committee faces a pivotal moment. Cassidy’s leadership and Kennedy’s stewardship of the nation’s health are both on trial. Public health advocates hope that, when the spotlight shines, Cassidy will put science and the well-being of Americans ahead of political calculation. As Dr. Benjamin put it, “I hope Dr. Cassidy shows up—and not Senator Cassidy.”
With the nation’s vaccine policy and public trust hanging in the balance, all eyes are on Capitol Hill as the drama unfolds.
