California. Lose that in June, no nomination. Lose it in November- eight years of waiting. Likely VP: Sanford- without two to three Southern states, November's gone. Daley controls the "Syndicate" bosses, who can completely reverse the equation with a couple of phone calls. 75% of the delegates are machine-controlled. RFK's campaign, though very ad-hoc, was outraising HHH by obscene margins (self-financing allowed) and was motivated. For McCarthy- he can release the delegates, because putting HHH over the top would be antithetical to his raison d'etre.
Now as to the debates: I must digress here.
Nixon is the better debater- their sparring over Genovese in 1965, Vietnam, the blood-to-NV comment, etc. More so: Nixon projects an aura of "cool" publicly. Privately, not so much. RFK is the reverse- he hated TV broadcasts. Richard Nixon did not publicly raise his voice, pound the podium, or allow civilians in such close proximity to (even holding) his person. Those polarity numbers, surpassing Hillary at her peak, are very personality-driven.
Especially the motorcades. If the average MC burb resident sees one older candidate delivering a speech on their needs, speaking in an indoor voice- they'll be sympathetic. Then we have the candidate who allows people to touch his person, take shoes and cufflinks (without precedent before or since), speaks very passionately, prefers the streets to canned indoor speeches, who do you think they'll vote for?
Now as for 1972: running against a popular incumbent Nixon in OTL conditions is a kamikaze act. Better to become Democratic Dictator, rebuild the organization, and wait for either Watergate (where he can replace Ervin) or 1976. There will likely be a phased US withdrawal from SVN and a reversion to supplying Thieu with proper equipment. On the domestic front: expect UHC similar to CHIP, increased emphasis on urban development, perhaps a go at Taft-Hartley. Foreign relations: relations with China, possibly with India. Likely re-elected in 1972 by a landslide if the economy and Vietnam hold. By 1976, likely Jackson v. Reagan. If RFK waits until 1976, he will be more focused on bread-and-butter domestic issues, deal with a crappy economy, and might lose in 1980. If he wins, then likely Bush Sr. succeeds him in 1984.