I'm not sure of the relationship between Biden and Southern Democratic senators back in the 1970's and 80's.
What I do believe is that an effective President must be willing to make deals with anyone. In this connection I want to recall one of my all-time favorite movies: Kelly's Heroes and Crapgame.
At the climax of the movie Don Rickles, as Crapgame, tells Telly Savalas, the wise old sergeant to make a deal. What kind of deal? A deal deal. The deal is made, and the Americans and the Germans split the gold in the bank. (You have to see the whole picture to understand the plot.)
Seriously, in my mind LBJ was the most effective president of my lifetime, and he was a dealmaker. I only regret he couldn't find his way to make the deal with the Chinese that Nixon did.
The point is, a deal usually brings together people whose interests conflict to some degree. I go to buy a car, I want the best car for the lowest price, the deal wants the highest price for the cars she has in stock. If we meet in the middle, we find the minimax, a deal which represents the best possible outcome for us both, even if it doesn't satisfy our maximum desires.
Bottom line: it bothers me to see Democratic candidates setting up barriers to dealmaking. Hopefully it's all or mostly political positioning, not to be taken seriously.