Two influential GOP senators are expressing unease over Health and Human Services Secretary Robert F. Kennedy Jr.’s firing of Susan Monarez as director of the Centers for Disease Control and Prevention (CDC), which led to the resignations of four other high-ranking CDC officials.

The strongest pushback among Republicans on Capitol Hill came Thursday from Sen. Bill Cassidy (R-La.), the chair of the Senate Health, Education, Labor and Pensions Committee.

He called on the department’s Advisory Committee on Immunization Practices (ACIP) to indefinitely postpone a Sept. 18 meeting in the aftermath of the staff shake-up at CDC.

“Serious allegations have been made about the meeting agenda, membership, and lack of scientific process being followed for the now announced September ACIP meeting,” Cassidy said in a statement.

Separately, Sen. Susan Collins (R-Maine) said she was “alarmed” by Monarez’s firing and echoed Cassidy’s call for congressional oversight over the decision to terminate her less than a month after her Senate confirmation.

“Susan Monarez is a highly capable scientist who brought a wealth of experience to the agency. While I recognize that the CDC Director serves at the pleasure of the President, I am alarmed that she has been fired after only three weeks on the job,” Collins said.

“Last night I talked with former Director Monarez about her removal. I agree with Chairman Bill Cassidy, who heads the Senate committee with jurisdiction over the CDC, that this matter warrants congressional oversight,” she added.

Cassidy warned the panel’s recommendations would “directly impact children’s health” and emphasized that “the meeting should not occur until significant oversight has been conducted.”

“If the meeting proceeds, any recommendations should be rejected as lacking legitimacy given the seriousness of the allegations and the current turmoil in the CDC leadership,” he said.

It’s unclear how far Cassidy, Collins or other GOP senators will go in challenging the moves, however.

The overwhelming majority of GOP senators have repeatedly sought to downplay major differences of opinion with President Trump and the most controversial members of his Cabinet this year, knowing that any criticisms of the president or his administration are certain to be met with a rebuke on Truth Social, Trump’s favorite instrument for keeping GOP lawmakers in line.

And both Cassidy and Collins are up for reelection in 2026.

GOP sources on Thursday predicted that Cassidy will be cautious in his approach to the controversy as he faces a conservative primary challenger, Louisiana Treasurer John Fleming, ahead of his 2026 reelection race.

Cassidy wants Trump’s endorsement and needs to tread carefully after he was one of seven Republican senators to vote to convict Trump on the impeachment charge of inciting insurrection during Trump’s 2021 Senate trial.

Collins, who also voted to convict Trump in that impeachment trial, is running for reelection in a state that voted for former Vice President Kamala Harris for president in 2024. That puts her in a different position from Cassidy.

The senators issued their statements after four senior CDC officials resigned from the agency following Monarez’s firing.

The four officials who resigned were Dr. Debra Houry, the CDC’s chief medical officer; Demetre Daskalakis, the agency’s top respiratory illness and immunization officer; Daniel Jernigan, a senior official who helped oversee responses to infectious diseases; and Jennifer Layden, who handled public health data.

Republican strategists warned the shake-up could underscore concerns that Kennedy is attempting to bend policy to fit a political narrative regardless of scientific reality.

One Republican strategist and former Senate GOP aide, who requested anonymity to comment candidly on the matter, said the shake-up at the agency in charge of protecting the nation’s health is proving to be an “epic” blunder.

“It’s a huge problem for CDC, for the country and for Kennedy’s credibility,” the strategist said. “He talked as if he just wanted transparency and to engage in a conversation and he’s clearly trying to cook the [books] on this point,” referring to Kennedy’s attempts to rewrite the nation’s vaccine policies.

“It seems like he’s planning on using very selectively curated, relatively opaque studies that don’t [meet] any type of normal standard of science to promulgate his view of what causes autism,” the source added.

Tom Frieden, who served as CDC director from 2009 to 2017 and is now president and CEO of Resolve to Save Lives, a global health organization, called Kennedy’s efforts to overhaul the agency an “assault” on science and sound health policy.

“It’s unprecedented. We’ve never seen the firing of a CDC director and the firing appears to have been triggered by the CDC director saying that they would not just put a rubber stamp on anything that [ACIP] said,” Frieden told The Hill in an interview.

“What we’re seeing here really is the use of ideology to make life-and-death decisions for our children. That’s unprecedented and it’s really dangerous,” he said. “I never thought I would see the day when we couldn’t rely on the CDC website for fact-based information and transparency about how it got put there, what it’s recommending and why.”

At the same time, the GOP strategist who spoke to The Hill downplayed how far any GOP resistance will go, though they predicted that Republicans could hold hearings that give Democrats a chance to get tough with Kennedy.

The strategist said Republicans can “thread the needle” by showing serious concern over Kennedy’s controversial moves without picking a fight with Trump over a core piece of his health care agenda.

One way to do that is to “have public hearings where Kennedy has to come and explain himself and put his science in public and let the world see and pick it apart,” the GOP source said.

Kennedy told Fox News’s “Fox & Friends” on Thursday that the CDC’s leadership “needs to execute Trump’s agenda” and said the agency “is in trouble” and “needs to be fixed.”

“CDC has problems. We saw the misinformation coming out of COVID, they got the testing wrong, they got the social distancing, the masks, the school closures that have done so much harm to the American people today,” he said.

White House press secretary Karoline Leavitt later on Thursday defended Trump’s decision to fire Monarez and said the president would nominate a new person to head the agency “very soon.”

Leavitt said that Trump “was overwhelmingly reelected on Nov. 5” and “this woman,” referring to Monarez, “has never received a vote in her life.”

“The president has the authority to fire those who are not aligned with his mission,” she said.

The administration on Thursday evening said Deputy Health and Human Services Secretary Jim O’Neill had been picked to serve as acting CDC director.

Daskalakis, who headed the center that issues vaccine recommendations, accused the political leadership at the Department of Health and Human Services of treating the “CDC as a tool to generate policies and materials that do not reflect scientific reality.”

The former senior health official criticized Kennedy’s decision to fire all 17 members of ACIP and replace them with people more aligned with his agenda.

In his resignation letter, which he posted on social media, Daskalakis said the reconstituted panel put “people of dubious intent and more dubious scientific rigor in charge of recommending vaccine policy to a director hamstrung and sidelined by an authoritarian leader.”

“Their desire to please a political base will result in death and disability of vulnerable children and adults,” he warned.

Two influential GOP senators are expressing unease over Health and Human Services Secretary Robert F. Kennedy Jr.’s firing of Susan Monarez as director of the Centers for Disease Control and Prevention (CDC), which led to the resignations of four other high-ranking CDC officials.

The strongest pushback among Republicans on Capitol Hill came Thursday from Sen. Bill Cassidy (R-La.), the chair of the Senate Health, Education, Labor and Pensions Committee.

He called on the department’s Advisory Committee on Immunization Practices (ACIP) to indefinitely postpone a Sept. 18 meeting in the aftermath of the staff shake-up at CDC.

“Serious allegations have been made about the meeting agenda, membership, and lack of scientific process being followed for the now announced September ACIP meeting,” Cassidy said in a statement.

Separately, Sen. Susan Collins (R-Maine) said she was “alarmed” by Monarez’s firing and echoed Cassidy’s call for congressional oversight over the decision to terminate her less than a month after her Senate confirmation.

“Susan Monarez is a highly capable scientist who brought a wealth of experience to the agency. While I recognize that the CDC Director serves at the pleasure of the President, I am alarmed that she has been fired after only three weeks on the job,” Collins said.

“Last night I talked with former Director Monarez about her removal. I agree with Chairman Bill Cassidy, who heads the Senate committee with jurisdiction over the CDC, that this matter warrants congressional oversight,” she added.

Cassidy warned the panel’s recommendations would “directly impact children’s health” and emphasized that “the meeting should not occur until significant oversight has been conducted.”

“If the meeting proceeds, any recommendations should be rejected as lacking legitimacy given the seriousness of the allegations and the current turmoil in the CDC leadership,” he said.

It’s unclear how far Cassidy, Collins or other GOP senators will go in challenging the moves, however.

The overwhelming majority of GOP senators have repeatedly sought to downplay major differences of opinion with President Trump and the most controversial members of his Cabinet this year, knowing that any criticisms of the president or his administration are certain to be met with a rebuke on Truth Social, Trump’s favorite instrument for keeping GOP lawmakers in line.

And both Cassidy and Collins are up for reelection in 2026.

GOP sources on Thursday predicted that Cassidy will be cautious in his approach to the controversy as he faces a conservative primary challenger, Louisiana Treasurer John Fleming, ahead of his 2026 reelection race.

Cassidy wants Trump’s endorsement and needs to tread carefully after he was one of seven Republican senators to vote to convict Trump on the impeachment charge of inciting insurrection during Trump’s 2021 Senate trial.

Collins, who also voted to convict Trump in that impeachment trial, is running for reelection in a state that voted for former Vice President Kamala Harris for president in 2024. That puts her in a different position from Cassidy.

The senators issued their statements after four senior CDC officials resigned from the agency following Monarez’s firing.

The four officials who resigned were Dr. Debra Houry, the CDC’s chief medical officer; Demetre Daskalakis, the agency’s top respiratory illness and immunization officer; Daniel Jernigan, a senior official who helped oversee responses to infectious diseases; and Jennifer Layden, who handled public health data.

Republican strategists warned the shake-up could underscore concerns that Kennedy is attempting to bend policy to fit a political narrative regardless of scientific reality.

One Republican strategist and former Senate GOP aide, who requested anonymity to comment candidly on the matter, said the shake-up at the agency in charge of protecting the nation’s health is proving to be an “epic” blunder.

“It’s a huge problem for CDC, for the country and for Kennedy’s credibility,” the strategist said. “He talked as if he just wanted transparency and to engage in a conversation and he’s clearly trying to cook the [books] on this point,” referring to Kennedy’s attempts to rewrite the nation’s vaccine policies.

“It seems like he’s planning on using very selectively curated, relatively opaque studies that don’t [meet] any type of normal standard of science to promulgate his view of what causes autism,” the source added.

Tom Frieden, who served as CDC director from 2009 to 2017 and is now president and CEO of Resolve to Save Lives, a global health organization, called Kennedy’s efforts to overhaul the agency an “assault” on science and sound health policy.

“It’s unprecedented. We’ve never seen the firing of a CDC director and the firing appears to have been triggered by the CDC director saying that they would not just put a rubber stamp on anything that [ACIP] said,” Frieden told The Hill in an interview.

“What we’re seeing here really is the use of ideology to make life-and-death decisions for our children. That’s unprecedented and it’s really dangerous,” he said. “I never thought I would see the day when we couldn’t rely on the CDC website for fact-based information and transparency about how it got put there, what it’s recommending and why.”

At the same time, the GOP strategist who spoke to The Hill downplayed how far any GOP resistance will go, though they predicted that Republicans could hold hearings that give Democrats a chance to get tough with Kennedy.

The strategist said Republicans can “thread the needle” by showing serious concern over Kennedy’s controversial moves without picking a fight with Trump over a core piece of his health care agenda.

One way to do that is to “have public hearings where Kennedy has to come and explain himself and put his science in public and let the world see and pick it apart,” the GOP source said.

Kennedy told Fox News’s “Fox & Friends” on Thursday that the CDC’s leadership “needs to execute Trump’s agenda” and said the agency “is in trouble” and “needs to be fixed.”

“CDC has problems. We saw the misinformation coming out of COVID, they got the testing wrong, they got the social distancing, the masks, the school closures that have done so much harm to the American people today,” he said.

White House press secretary Karoline Leavitt later on Thursday defended Trump’s decision to fire Monarez and said the president would nominate a new person to head the agency “very soon.”

Leavitt said that Trump “was overwhelmingly reelected on Nov. 5” and “this woman,” referring to Monarez, “has never received a vote in her life.”

“The president has the authority to fire those who are not aligned with his mission,” she said.

The administration on Thursday evening said Deputy Health and Human Services Secretary Jim O’Neill had been picked to serve as acting CDC director.

Daskalakis, who headed the center that issues vaccine recommendations, accused the political leadership at the Department of Health and Human Services of treating the “CDC as a tool to generate policies and materials that do not reflect scientific reality.”

The former senior health official criticized Kennedy’s decision to fire all 17 members of ACIP and replace them with people more aligned with his agenda.

In his resignation letter, which he posted on social media, Daskalakis said the reconstituted panel put “people of dubious intent and more dubious scientific rigor in charge of recommending vaccine policy to a director hamstrung and sidelined by an authoritarian leader.”

“Their desire to please a political base will result in death and disability of vulnerable children and adults,” he warned.