If Joe wants the active support of progressives, rather than just getting as many of them as possible to vote for him with gritted teeth by having his surrogates verbally bludgeon them into voting by simply DEMANDING their votes, here are some things he could do to reach out to them:

1) He could admit that his "I'm the ONLY one who can win" pitch in the primaries was arrogant and unjustified, since the polls showed that virtually all the other candidates were polling just as strongly against Trump as he was;

2) He could say " look, as you know, I'm not a 'socialist', but I accept that it is valid for those who identify with that word to do so, and I share with them the conviction that life should NOT be about nothing but short-term financial gain for the already rich;

3) He could make it clear that, while he identified with the militarist wing of the party for much of his career, he recognizes that this is a time when the U.S. should cut the war budget, reallocate a significant amount of funds devoted to it to deal with the pandemic, other healthcare issues, housing, jobs programs and other human needs. This would take Trump's "I kept us out of any new wars" argument away from him.

4) finally, he could say something like this "I will have my priorities as president and they may not always be yours, but if you can get something through congress on your own, I will sign it".

Joe would lose nothing from any of that.