Newburyport, Mass. — Every year on the third Monday of January, Americans of all races, backgrounds and ideologies celebrate the Rev. Dr. Martin Luther King Jr. He is rightly lionized and sanctified by whites as well as blacks, by Republicans as well as Democrats.

It is easy to forget that, until fairly recently, many white Americans loathed Dr. King. They perceived him as a rabble rouser and an agitator; some rejoiced in his assassination in April 1968. How they got from loathing to loving is less a story about growing tolerance and diminishing racism, and more about the ways that Dr. King’s legacy has been scrubbed and blunted.

The Dr. King we remember today is particularly at odds with his radical turn in his last years. In 1967 he denounced the Vietnam War and warned that America was courting “spiritual death.” In early 1968 he planned the Poor People’s Campaign, in which millions of impoverished Americans — black, white and Latino — would gather in Washington for an enormous demonstration. He called for $30 billion annually in antipoverty spending, and asked Congress to guarantee an income for each American. To many Americans, this sounded like socialist lunacy.

Dr. King spent his final days in Memphis, marching with striking sanitation workers. On March 28, 1968, some marchers behind him turned violent. His critics believed their argument had been proved — that Dr. King’s claims to nonviolence were so much pretense. When he was killed a week later, Senator Strom Thurmond, Republican of South Carolina, told an audience that Dr. King was “an outside agitator, bent on stirring people up.” Ronald Reagan, then governor of California, described Dr. King’s killing as a “great tragedy that began when we began compromising with law and order, and people started choosing which laws they’d break.”