Sen. Bill Cassidy (R-LA), chairman of the Senate Health Committee, directly challenged President Donald Trump's vaccine messaging on CBS's 'Face the Nation,' questioning the basis for the president's claims and warning that discouraging immunization could trigger outbreaks.

Cassidy, a physician, called Trump's previous characterization of the measles vaccine as lethal "absurd" and demanded to know where the president was getting his information. "If you really don't have it, why are you willing to risk the lives of fellow Americans?" Cassidy asked.

Trump has outlined a plan to split childhood vaccines into five doses, claiming the change would reduce autism. "We're also going to be demanding the drug companies make their doses in 20 percent shots. So you have shot one, shot two, shot three, shot four, shot five. I think you're gonna see a massive reduction in autism," Trump said.

Cassidy said he did not know which specific vaccines Trump was referring to or whether manufacturers would comply. He called for "radical honesty" from the administration on vaccine policy.

The senator emphasized that vaccines "are safe" and have been proven safe through scientific evaluation. He warned that if Trump continues to discourage immunization, measles cases and deaths could increase across the country.

Cassidy confirmed his support for Dr. Nicole Saphier, Trump's Surgeon General nominee, after she told lawmakers the vaccine is safe and people should be vaccinated. But he placed a condition on backing FDA commissioner nominee Dr. Heidi Overton: she must acknowledge that calling the measles vaccine lethal was wrong.

Cassidy cited specific public health dangers, pointing to measles exposure incidents at Children's Hospital of Philadelphia, including a case where a child with active measles entered a neonatal intensive care unit. He referenced four deaths in Pennsylvania, distinguishing between deaths directly caused by measles and those merely associated with the disease.

Cassidy concluded by saying Trump should tell Americans directly: "Be vaccinated. It is safe and effective." He added that confusing public messaging on vaccines could hurt Republicans with women voters, who typically make health decisions for their families.