The ghost of Robert F. Kennedy has lingered over the Democratic presidential race this year in more ways than one. Most recently, it was conjured by Sen. Hillary Clinton, who was criticized for referring to Kennedy's assassination as an example of how quickly things can change in the race for a party's nomination. In a larger sense, however, many have raised parallels between the young, articulate and energizing Kennedy and Barack Obama, who some see as possessing the same attributes.

Ghosts can be difficult to see clearly.

Kennedy was fatally shot 40 years ago Thursday in a Los Angeles hotel, shortly after gaining a narrow victory in the California primary. Modern folklore has him riding the crest of a wave toward the nomination when he died, but that was not so. As far as the race of '68 was concerned, the modern parallel is more that of Clinton than Obama. Kennedy was a long-shot who might have pulled off victory at the convention, but Hubert Humphrey had the inside track.

Still, nothing jars and offends the soul of democracy more than a political assassination. In a land where the people hold power collectively, the thought of someone with a gun trumping everyone's vote is a staggering affront. And so the RFK assassination remains an icon of that age.

Forty years later, it is easy to forget the tenor of those times. RFK's death was not isolated. It came less than two months after the assassination of the Rev. Dr. Martin Luther King Jr. and less than five years after the assassination of President John F. Kennedy. It came amid anti-war riots on college campuses, race riots in the streets of many American cities and persistent challenges to social order and long-held values.

Within hours of the death of Robert Kennedy, the BBC in Britain broadcast a supplication that said, "We pray for the American people that they may come to their senses."

That was the prayer of many in the United States, as well.

Today, echoes from that time still linger. The nation is ideologically divided along lines that roughly equate to the roiling issues of 1968. But, despite another unpopular war, today's political and social landscape is much calmer.

On Tuesday, Obama became the first black man ever to clinch the nomination of a major political party in a race for the White House. That would have been unthinkable 40 years ago. Times have indeed changed.

And yet, in other ways times have barely budged. A young Palestinian was arrested and convicted of killing Kennedy. Ties were drawn between the crime and Kennedy's support for Israel. Then, as now, the Middle East looms above American politics as a great unsolvable enigma.

Today, as then, people worry about candidates being shot before the people can choose.

The British prayer from all those years ago remains valid. Placed against the backdrop of a long-ago age of turmoil, Americans must hope they have, in many ways, come to their senses.