Wow.. that dredged up an old memory... wasn't it Max Rafferty who took him out in the primary?
Yup. And then a lot of the GOP establishment was loathe to support Rafferty, who then lost to the execrable Alan Cranston. Had Kuchel won renomination and reelection, he would’ve become Republican Senate Leader upon Everett Dirksen’s death in September 1969 (as he had been Minority Whip since Dirksen was elevated in 1959 after Bill Knowland made his ill-advised attempt to switch offices with Gov. Goodwin Knight).
As bad as we think of our RINOs today, we had a real motley crew of ultra-Socialist Republican Senators in those days (Kuchel, Brooke, Mathias, Case, Javits, et al), some voting identical to or even to the left of the most far-left Democrats (such as Ted Kennedy, who was at least pro-life in the early days).