After serving in the government, he became a prominent political commentator. “Centrism doesn’t mean splitting the difference,” he said in 2020.

David Gergen, an inside-the-Beltway veteran who helped shape the public images of four presidents, mostly Republicans, and who, after a turn as a magazine editor, trod a well-worn path from political insider to television commentator, died on Thursday in Lexington, Mass. He was 83.

His death, at a retirement community, was caused by Lewy body dementia, his son, Christopher, said. Mr. Gergen previously lived in Cambridge, Mass.

It was Mr. Gergen who devised a line in the 1980 presidential election that helped secure victory for the Republican candidate, Ronald Reagan, over Jimmy Carter, the incumbent Democrat. In that era of high inflation, onerous interest rates and a national psyche wounded by Iran’s holding of 52 Americans hostage, Mr. Carter was already on the ropes. The clincher came in a televised debate a