Senator John Milkovich reads amendment #296 during the Senate Chamber meeting in Baton Rouge on Sunday, June 3, 2018.

Republican U.S. Sen. Bill Cassidy mostly left medicine behind when he went to Congress. He still has that M.D. beside his name, though, so when he speaks on things like the importance of vaccination, his fellow politicians should listen.

The shame of the matter is that he has to keep speaking at all.

Cassidy spoke when fellow U.S. Sen. Rand Paul, a Kentucky Republican and a fellow physician, sided with anti-vaxxers in a recent Senate hearing. Paul said he understands the benefits of vaccination and said he and his kids were vaccinated. But he criticized mandatory vaccinations, saying that “I still don’t favor giving up on liberty for a false sense of security.”

Cassidy responded by citing his own experience as a gastroenterologist in Louisiana’s old Charity Hospital system.

Grace Notes: In battle of the Senate docs, Bill Cassidy crushes Rand Paul's anti-vax argument

“I’ve seen people who’ve not been vaccinated who’ve required liver transplantation because they were not, and/or who ended up with terrible diseases because of no other reason than they just, for whatever reason, didn’t understand vaccination was important,” he said.

Cassidy spoke again this week when state Sen. John Milkovich, a Democrat from Shreveport, went way off the rails on the Senate floor. If Paul’s comments were offensive because he surely knows better, Milkovich, who flogged one debunked, conspiracy-minded theory after another, revealed himself as a shockingly ignorant know-nothing.

“There is a very contentious scientific debate that’s going on right now in America and has been for decades,” Milkovich said. “Many are saying that these vaccinations pose danger.”

“For example, when (I was) growing up autism did not exist,” he continued. Milkovich also claimed that tissue from aborted fetuses is used to create vaccines and that they spread dangerous neurotoxins.

That’s preposterous, and Cassidy chimed in from Washington to call the diatribe “fake news.” He also pointed out that parents who refuse to vaccinate their kids put others at risk: “If your child was vulnerable, you’d want everyone else to be immunized.”

Sen. Bill Cassidy defends vaccines after state lawmaker makes autism claims: 'That's fake news'

This isn’t an academic argument. Measles cases have topped 700 nationwide, according to the Centers for Disease Control and Prevention, the highest figure in decades. This is a public health emergency that could have and should have been avoided, and it’s particularly irresponsible to someone speaking under the authority of an elected position to spread misinformation.

Nor should it take a medical degree to understand the implications, just a minimal ability to think critically and behave responsibly. Which is apparently too much to ask of some politicians.

Follow Stephanie Grace on Twitter, @stephgracela.