Absolutely. Kennedy was in trouble in the polls. The pubbies were split, and Goldwater always came across as a cranky old guy, but Kennedy getting assassinated was the best thing that ever happened to Johnson politically.
That meshes with the theory that LBJ himself was a player in the JFK assassination. There's some pretty good overall evidence to support that in a book by Barr McClellan (estranged father of one of W's WH press secretaries) titled "Blood, Money, and Power."