“Rockwell’s greatest sin as an artist is simple: His is an art of unending cliché.”

In that Washington Post criticism of a 2010 exhibition of Norman Rockwell paintings at the Smithsonian, Blake Gopnik joined a long line of prominent critics attacking Rockwell, the American artist and illustrator who depicted life in mid-20th-century America and died in 1978.

“Norman Rockwell was demonized by a generation of critics who not only saw him as an enemy of modern art, but of all art,” said Deborah Solomon, whose biography of Rockwell, “American Mirror,” was published last year. “He was seen as a lowly calendar artist whose work was unrelated to the lofty ambitions of art,” she said, or, as she put it in her book, “a cornball and a square.” The critical dismissal “was obviously a source of great pain throughout his life,” Ms. Solomon, a frequent contributor to The New York Times, added.