In a tense exchange with Senator Bill Cassidy, a Republican from Louisiana, Robert F. Kennedy Jr. displayed a surprising lack of familiarity with Medicare and Medicaid, the government programs responsible for covering more than 150 million Americans.

At times, Mr. Kennedy seemed to confuse the two programs. Medicare is a federal program that provides coverage to older and disabled Americans, while Medicaid is a state-federal program that covers low-income people.

When he first described Medicare, he seemed to ignore the half of the Medicare program that relies on private insurance plans to provide care. Later, he acknowledged that he was enrolled in a private Medicare Advantage planand said he thought “more people would rather be on Medicare Advantage because it offers very good services.”.

Medicare Advantage plans have been heavily criticized by lawmakers, including by federal regulators Mr. Kennedy would oversee if confirmed and by public advocacy groups. They argue that the plan overcharges the government and delays and denies access to care.

Mr. Kennedy described Medicaid as ”fully paid for by the federal government.” In fact, Medicaid, which provides health insurance coverage to nearly 80 million low-income Americans, is financed through a combination of state and federal funds.

Mr. Kennedy also claimed that many Medicaid enrollees were frustrated by high costs they face with their public insurance coverage.

”Most people who are on Medicaid are not happy,” Mr. Kennedy claimed. ”The premiums are too high. The deductibles are too high.”

But the vast majority of Medicaid enrollees do not pay any premiums or deductibles for their coverage. Federal law specifically prohibits premiums for the lowest-income Medicaid enrollees. Patients typically do not have to pay anything when they go to the doctor, aside from a handful of state-based experiments that have tested out small fees.

Senator Cassidy asked Mr. Kennedy to describe how he would reform the Medicaid program. While other Trump nominees have offered concrete policy proposals — Russell Vought, the nominee to run the Office of Budget and Management, suggested a work requirement for the program in his confirmation hearing last week — Mr. Kennedy described vaguer changes.

He said he supported changes to “increase transparency” and” “increase accountability.”

When Mr. Cassidy pressed him to be more specific, Mr. Kennedy responded, “I don’t have a broad proposal for dismantling the program.”