It's pretty clear from context.

Also, OP's ignoring that Kennedy was also a progressive hero, too. The primary was progressive vs. progressive-- which is part of the reason it's remembered today as the poster child of pointless infighting that did nothing but benefit the opposition. I've literally never heard anyone here in the States have OP's take on the primary until this thread.

I explicitly said the problem was the party leaders allowing a primary.

That was “moderate” party leaders trying to sabotage a progressive at any cost.

That fucked America up reeeeeeeally badly. But the people who decided to do it got what they wanted: an excuse to tell voters that progressives can’t win.

Sink two progressives in one blow, and hope you get a moderate in 4 years.

If Carter did 8, Kennedy would have likely been president next, maybe for another 8 years. Moderates were losing the party. Having a republican beat a weakened Carter let them tell voters that the party had to move right and that progressives couldn't win.