Joe Kennedy III, the former Democratic congressman from Massachusetts, gazed out his window at endless fields of cotton and soybeans as he drove across the Mississippi Delta one sweltering afternoon last month. He was a long way from home, but in a sense returning to it.

“People living here have been receiving boil-water notices for two years now,” he said, using an expletive. “We should be banging the drums on this every day.”

Mr. Kennedy, 44, was retracing the steps of his grandfather, Robert F. Kennedy, the former attorney general and candidate for president, who toured the Delta in 1967 and encountered the kind of hunger and poverty more often associated with the developing world. “Those images Bobby took away of children with bloated stomachs and open sores had a huge impact on him,” said Evan Thomas, a biographer of both the elder Kennedy and his brother, President John F. Kennedy.

Mr. Kennedy nodded to the history. “I know a bit about my grandfather’s visit to the Delta back in the ’60s, and how it changed and outraged him to see this in the richest country in the world,” he said. “I’m proud that my family has spent a lot of their years in office advocating for these people.”

Mr. Kennedy is on a mission to continue the legacy of an American political family that has in recent years lost some of its liberal luster. It angers him that his uncle Robert F. Kennedy Jr., the health and human services secretary, is a key figure in an administration that is overturning core values of his family.

The health secretary has defended work requirements for Medicaid recipients, “which do not work,” the younger Mr. Kennedy said. “The only thing they succeed at is kicking people off Medicaid who need it.”