If he was alive today he’d shift as necessary. Leading BLM parades. Past associations would be dismissed like KKK Byrd.
No chance Gene McCarthy would have been the rat nominee in 1968 no matter the circumstances. Bobby Kennedy only had a chance cause he was Kennedy, Humphrey was really in the driver’s seat with the party bosses still choosing the nominee.
We’ll see. I’ve seen plenty of left-wing guys who refused to support certain left-wing causes precisely BECAUSE they realized it was something they wouldn’t support. Case in point, Martin Sheen refused to back any abortion-supporting president, famously even refusing to back Barack Obama, precisely because the latter was openly pro-Abortion.
Besides, Bobby Kennedy as you pointed out was a hard-core McCarthyite, which if anything would have been political suicide at the time for leftists (let’s not forget that Nixon, himself a McCarthyite, was repeatedly pillored before being forced to resign in disgrace precisely because he nailed Alger Hiss, and that was despite moving to the left by the time he was in the presidency), same goes with JFK. But yeah, I will agree that Kennedy probably would not have lasted long in the presidency (still more of an anti-Commie than Harry Truman and FDR, though.).