The Republican senator John Kennedy accused Joe Biden of “demagoguing” the issue of how to fund social security and Medicare and protecting the two programs from Republican proposals to cut them, calling it a “very immature thing to do”.

Speaking to Fox News Sunday, Kennedy took aim at Biden for mentioning in his State of the Union address last month that some Republicans have proposed to “sunset” social security and Medicare as part of attempts to balance the federal budget.

“The problem is that President Biden in his State of the Union Address decided to demagogue the issue,” the Louisiana senator said. “We all saw it.

“He basically said, ‘If you talk about social security or Medicare, I’m going to call you a mean, bad person.’ And that just took the issue off the table when the president decided to demagogue it … You can only be young once, but you can always be immature, and I thought it was a very immature thing to do.”

In his speech to Congress, Biden, 80, drew boos from some Republicans when he said some wanted social security and Medicare to “sunset”, meaning face periodic re-authorization without which they would close.

“Anybody who doubts it, contact my office, I’ll give you a copy of the proposal,” the president said.

The far-right Georgia representative Marjorie Taylor Greene yelled: “Liar!”

Biden was widely praised for using the moment to steer Republicans into cheering the idea of social spending.

“As we all apparently agree,” he said, “social security and Medicare are apparently off the books now … We’ve got unanimity!”

Biden has since promised repeatedly to protect the two programs, shaping the threat of cuts as a central campaign issue as he readies an announcement that he will run for re-election in 2024.

On Thursday, during his introduction of his federal budget proposal, Biden used shorthand for Donald Trump’s campaign slogan when he said: “I won’t allow [social security and Medicare] to be gutted or eliminated as Maga Republicans threaten to do.”

The budget proposal, which includes a 10% increase for the Social Security Administration, drew Republican fire.

Kennedy criticized the $6.8tn package, which also includes tax raises for wealthy corporations and individuals and is meant as a position statement ahead of talks aimed at avoiding a US debt default.

“The president’s budget took my breath away,” Kennedy said. “His numbers are extraordinary. We’re going to run out of digits here.

“The president says that his budget will solve our financial problems in Medicare and social security … That’s not true. Anything seems possible when you don’t know what you’re talking about … The only way I know how to improve the president’s budget is with a shredder.”