I lived through the assassination of Pres. Kennedy. Because I was a Republican political operative at the time I have a different perspective on Pres. Kennedy and the subsequent history.
First of all, Pres. Kennedy was not a divine creature in my mind. He was a fanatic fan of unions, a hater of big business and he was strongly disliked by most Americans. He was disliked only a little less than Richard Nixon. He won the 1960 election by fraud in Illinois and Texas. I also knew during his presidency of his profligate use of women. I even knew one woman who had had sex with him and his brother (separately).
All of which is to say that I did not come under the preposterous veil of ignorance and fantasy known as Camelot after Kennedy was assassinated.
The most significant post-Kennedy effect of the assassination was the passage of two civil rights bills by his successor Lyndon Johnson. Jack Kennedy could not have passed the civil rights bills. The Democratic Party had already destroyed the civil rights bills introduced by president Eisenhower. Johnson used the tragic assassination of Kennedy to manipulate a few Democratic party legislators. Only a few Democrats were needed when combined with a majority of the Republican legislators to pass the civil rights bills.
Up until Johnson's two civil rights bills, the Kennedy brothers had ignored and deflected all of the civil rights movements. There was nothing they could do because they were elected by the Southern Democrat's. The Southern Democrat's were a backbone of the Democratic Party. Johnson was willing to restructure the Democratic Party.
Among the most consequential effects of the Johnson civil rights legislation was that the Dixiecrat's left the Democratic party. This gave the presidency to Richard Nixon and the Republicans. It created a realignment in the Democratic Party. The Democrats had to run a Southerner (Jimmy boy Carter) for their only presidential win in the succeeding 24 years.
It is because of this that I credit Lee Harvey Oswald with the inadvertent creation of the civil rights legislation and the ending of the decent part of the civil rights movement.
There is no way to write alternative histories without Lee Harvey Oswald but if there were an alternative history of the civil rights movement it would have taken much longer and remained in the Republican Party.