To a degree, although he had his own opinions and was a front runner OTL before he was assassinated.
But that was several years after his brother assassination, he had time to show the country he was not only the brother of the president but himself.
Just taken a look at his wiki entry, Robert_F._Kennedy. He was not only Attorney General but seems to have a pretty liberal agenda, opposing the Vietnam war and wanted more done on racial equality so could end up as the champion of that cause.
Also the man who assassinated him in 1968 was a Palestinian who was angry at his support for Israel in the 6 days war so he's not going to get assassinated by him before the 1964 election.
Not saying he would be the Demcoratic candidate let alone winning but sounds like he would be likely to be a significant figure.