Both Republicans and Democrats clash with RFK Jr. on vaccines, CDC turmoil

Most Democrats on the Senate Finance Committee -- which has oversight over HHS and is questioning Kennedy today -- put out a statement before Tuesday's hearing calling for RFK Jr's resignation.

"Robert Kennedy has failed to protect the health of the American people and endangers the lives of all Americans, particularly children, people with disabilities, and vulnerable Americans. Robert Kennedy must resign, and if he doesn’t, Trump should fire him before more American families are hurt by his reckless disregard for science and the truth," the group of 12 senators wrote.

Kennedy avoided reporters' questions before the hearing started, as did Republican Sen. Bill Cassidy.

Democratic Sen. Mark Warner who signed the letter, however, stressed his calls for Kennedy's removal.

"Absolutely. Purely based on the fact that he's completely gone against what he pledged to this committee and to my friend Bill Cassidy," he told ABC News.

-ABC News' Jay O'Brien and Allison Pecorin

Kennedy said former CDC Director Susan Monarez lied in her op-ed published in the Wall Street Journal on Thursday morning, in which she detailed the pressure she faced from Kennedy.

Monarez wrote that in that meeting, she was "told to preapprove the recommendations of a vaccine advisory panel newly filled with people who have publicly expressed antivaccine rhetoric ... It is imperative that the panel’s recommendations aren’t rubber-stamped but instead are rigorously and scientifically reviewed before being accepted or rejected."

"Did you in fact, do what Director Monarez said you did, which is tell her just go along with vaccine recommendations even if she didn't think such recommendations aligned with scientific evidence?" Democratic Sen. Ron Wyden asked Kennedy.

"No, I did not say that to her, and I never had a private meeting with her," Kennedy said.

"So she's lying today to the American people in the Wall Street Journal?" the senator asked.

"Yes, sir," Kennedy said.

Monarez's lawyer pushed back on Kennedy's claims, calling them "false" and "patently ridiculous."

"Dr. Monarez stands by what she said in her op-ed in The Wall Street Journal, would repeat it all under oath and continues to support the vision she outlined at her confirmation hearing that science will control her decisions," her lawyers, Mark Zaid and Abbe Lowell, said in a statement.

Kennedy said that he received latest numbers from the CDC that 76.4% of Americans now have a chronic disease.

"This is stunning … This is a national security issue," he said. "When my uncle was president, we spent zero on chronic disease. We [have now] spent $1.3 trillion."

Kennedy claimed this is why peopled needed to be fired at the CDC, saying they "didn't do their job" to keep Americans healthy.

Before facing questions from lawmakers, Kennedy took a moment in his opening statement to address recent turmoil at the CDC.

"These changes were absolutely necessary adjustments to restore the agency to its role as the world's gold standard public health agency with the central mission of protecting Americans from infectious disease," Kennedy said.

He said the agency needed "new blood" and criticized its response to the COVID-19 pandemic. Many public health experts argue that politics and social resistance hampered the CDC's efforts to quell the pandemic and save lives.

Last week, Susan Monarez was ousted from her role as CDC director over her resistance to changes on COVID vaccine policy. Four top CDC officials then resigned in protest.