Actually Bobby Kennedy appeared to be largely 'borrowing' Gene McCarthy's message. McCarthy had seriously wounded LBJ in the early primaries. It was only after this was evident that Bobby jumped into the race, with a campaign that echoed McCarthy's opposition to the Vietnam War.
He may have borrowed, as any genius must build on the existing or be so eccentric as to become irrelevant after his fifteen minutes, and after borrowing changed the expression into his own. He was in a way like Xenophon the stenographer become the general, with the group captains saying, you've got the stuff, go for it.