Image copyright Getty Images

After Martin Luther King was killed, many believed senator and presidential hopeful Robert Kennedy was going to carry on the reforming fight. Fifty years on, some argue Kennedy's assassination had a profound impact on the direction of America.

When Robert Kennedy was shot in the crowded kitchen passageway of Los Angeles's Ambassador Hotel, photographer Ronald Bennett leapt onto a stainless steel food cart to see from above and photograph the ensuing chaos.

As people shouted, screamed and wrestled with shooter Sirhan Sirhan, Bennett suddenly found himself in a position to intervene.

"They couldn't get the gun out of his hand, he obviously had a lot of adrenaline flowing through him, so I stamped on his hand and they got the gun," says Bennett, who was working for United Press International (UPI) at the time.

"As I popped another roll in the camera, I realised I had already taken about 25 pictures on sheer automatic reflex."

Kennedy had been celebrating winning the California primacy in the race to become the Democratic nomination for the presidential election later that year.

But now the senator was sprawled on the floor barely conscious, with one eye open and one eye closed - a bullet had entered his head.

The police arrested Sirhan and Kennedy was rushed to hospital, leaving Bennett amid the ruins of a celebratory party turned nightmare.

"People were wandering aimlessly, some cried, others merely sagged to the floor or they stood moaning, praying, rocking on their heels like children in disbelief," says Bennett.

Image copyright Ron Bennett photographic archive Image caption Bennett helped to secure the gun then started taking photos

Kennedy died of his wounds 26 hours later, leaving the question 50 years later of how America might have been different if Kennedy had lived and gone on to win the presidency.

Coming less than two months after Martin Luther King Jr's assassination, for many Kennedy's death ended the revival of American liberalism.

"King had prepared us for his death, and after it [MLK's death] happened, there was no weeping, we immediately started figuring out how we were going to carry on the Poor People's Campaign," says Andrew Young, one of King's closest aides.

But that maintenance of effort was scuppered by Kennedy's death.

"That was when I broke down," says Young. "I think that the rational liberal democratic socialist view of the world, from Franklin Roosevelt all the way to Lyndon Johnson, was really cut short by the assassinations of Martin Luther King and Robert Kennedy."

The loss of such strong voices advocating traditional liberal policies also meant there was no-one to counter emerging criticism of those polices from the likes of Richard Nixon and then Ronald Reagan, argues Jeremi Suri, a history professor and author.

Image copyright Getty Images Image caption Kennedy's death announced in Rome

"American would certainly be different today had Kennedy lived," says Suri. "We would not have had as strong a swing to the right, and the partisanship in our society now would look different."

Suri says that if the disillusionment in the Democratic Party in the 1970s - discrediting many traditional policies - had not happened, there would not have been a Jimmy Carter presidency and probably not a Bill Clinton one either.

Carter and Clinton were Democrats who moved away from traditional LBJ-style government programmes, he says. And they wanted to show that they were making government smaller, not bigger. This meant they were less interventionist in personal choices about issues like gun ownership and local control of schools.

"Historical conjecture is a tricky business full of uncertainty, but history is ultimately about causality - and we value historical causes differently because of the 'what-ifs' involved," says Ben Wright at the Dolph Briscoe Center for American History that houses Ronald Bennett's photographic archive.

"Events like the assassination of Dr King and Senator Kennedy matter precisely because we intuit so many significant possibilities for the trajectory of American history had things turned out differently."

Image copyright Getty Images Image caption Family gather at Robert Kennedy's grave, 11 years later

Whether Robert Kennedy could have kept the Democratic Party together, let alone secured its nomination in 1968, will always remain debatable - but some who were there with Kennedy when he was shot remain convinced his unique political talents could have taken him to the presidency.

"His personality and appearance generated an inspiring figure to people and an almost desperate desire to restore things that were taken away from the country with the death of his brother and the Vietnam War," says Jules Witcover, a journalist covering Kennedy's campaign.

"Nobody in the white community had been able to establish a rapport with the black community before Robert Kennedy."

Media playback is unsupported on your device Media caption The divided visions of Robert Kennedy and Martin Luther King

Others, however, note the significant political and societal odds that were stacked against Kennedy.

"By the end of the 1960s, the forces that were swelling up against the Great Society, which was an extension of the New Deal of the 1930s, were going to defeat whoever the Democrats put up," says HW Brands, historian and author.

"Americans were disillusioned and angered by the violence of the 1960s, and by the failure of the Democratic governments of John Kennedy and Lyndon Johnson to take Vietnam to a successful conclusion."

Brands notes how also the Civil Rights movement had largely achieved its legislative aims, and so if either Martin Luther King Jr or Robert Kennedy had lived they would have had to battle the great American conundrum of economic inequality and poverty that has thwarted all others.

Image copyright Getty Images Image caption Kennedy meets voters in Harlem, New York, in 1964

"That's a much tougher nut to deal with going off the last 50 years of American politics," Mr Brands says.

"You can repeal laws against blacks, but can you mandate economic equality? Nobody's figured out how to do it… for a society that is organised economically along capitalist lines."

The whole experience of his campaign and what he stood for remains a milestone for the Democratic party, says Witcover, who went on to write 1968: The Year the Dream Died and a book about Kennedy's campaign.

The Democratic National Convention that followed Kennedy's death in August descended into violence and farce, delivering a blow the Democrats have been reeling from ever since.

Now it is the turn of the Republican Party to go through an identity crisis as it grapples with the impact of Trump's unorthodox approach.

Image copyright Getty Images Image caption Mugshots of Sirhan Sirhan

"The modern comparison with 1968 is 2016," Mr Wright says. "In many ways 2016 doesn't hold a candle to 1968, but both were characterised by political upheaval, social divisions, racial issues and a general perception of decline."

Both Bennet and Witcover remember Kennedy warmly as a politician who had a Midas touch with people from all walks of life.

"He was the last politician who came from a background of Franklin Roosevelt-influenced social welfare policies who could connect with rural voters," Mr Suri says.

"What ended in the late 1960s and early 1970s was a set of policies of expanding rights, expanding government services and assistance for those in need, and the backlash against that was facilitated by the absence of effective figures like Robert Kennedy."