It was the biggest night of the young presidential candidate's campaign. In the South Dakota primary, he had trounced that state's native son, the sitting vice president, while in California he had just defeated the Minnesota senator who, one week earlier in Oregon, had inflicted his first-ever election defeat.

After accepting the cheers and applause of the crowd in the Embassy Room, he moved through a kitchen corridor on Los Angeles' Ambassador Hotel on his way to a press conference. He turned to touch the outstretched hand of Jesus Perez, a 17-year-old busboy, just before the assassin's bullet from a snub-nosed Iver Johnson revolver pierced his skull and smashed into 42-year-old Sen. Robert F. Kennedy's brain. He would die 25 hours later at Good Samaritan hospital on June 6, 1968.

For those of us who were alive then, the memory of those days is as clear and as painful as yesterday. Why did Robert Kennedy, a man who was never nominated, let alone elected, president, touch so profoundly — and so permanently — so many people? And why has no candidate since been able to inspire both the same passion and to enkindle the same public fervor for racial and social justice?

Here's my theory, which you have every right to know, comes from the frankly nonobjective view of somebody who, before he became a reconditioned virgin and a "detached" journalist, worked as a campaign organizer for Kennedy in the Nebraska, Oregon and California primaries.

American voters are always searching for one of two presidential types — a Warm-Hearted Conservative and-or a Tough, Muscular Liberal. Robert Kennedy, in my judgment, was quite simply the last Tough Liberal.

He was not a compelling orator. His platform manner could be tentative, his voice unimposing. But he was without pomposity, and he struck no false notes. He was small, maybe 5 feet 9 inches, and almost surely by the time of the California primary not weighing over 150 pounds. He had the strong, muscled forearms of the athlete he was, but he often slouched when he walked. He grew up behind two golden, charmed brothers, both sent to early graves — one in heroic wartime service and the second, the nation's commander in chief, assassinated in Dallas.

Tragedy had tested Robert Kennedy, and he had more than passed that test. He was the only American presidential candidate of the post-Civil Rights era who was able to win the enthusiastic — make that the devoted — backing and trust of both white working-class Democrats and African-American Democrats. He could speak of law and order to black audiences and they would listen, because they knew he was not talking in the racial-political shorthand of a Richard Nixon. White ethnic voters knew that he was not your garden-variety, "can't we all get along" liberal, that he was tough as nails and that nobody — CEO or labor boss or foreign dictator — could lean on Bob Kennedy.

Children loved Robert Kennedy, a feeling he returned fully to each child he encountered. He spoke to and for the Left-Out and the Left-Behind, poor white Americans in the hollows of Eastern Kentucky, poor black Americans in the ghettos of Oakland, poor brown Americans in the barrios of Los Angeles, poor Native Americans on the Dakota reservation.

The late Fred Dutton, the gifted California advisor who was constantly at the candidate's side, may have put it best: "Bob Kennedy is the kind of guy I'd like in a foxhole with me. He wouldn't run when the shooting began."

This was not the 2 o'clock courage of the whisky warrior. As a 21-year-old infantryman, Dutton fought for two months in the snow at the Battle of the Bulge, where he earned a Purple Heart and the Bronze Star, and was captured by the Germans and held as a POW.

Robert Kennedy was tough enough to beat Richard Nixon in 1968. He was truly the Last, Tough Liberal.

To find out more about Mark Shields and read his past columns, visit the Creators Syndicate web page at www.creators.com.

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