I thought I had read somewhere that Obama had the most liberal voting record and Biden was second, but maybe that source was incorrect. Different groups take different votes to evaluate politicians by so it could be that different organizations rate Biden further to the left and others more to the center of the Democratic pack...which of course is almost completely left of center.
Senators who are running for president miss a lot of votes and only show up when the party really needs them, so there was talk when Obama (and before him Kerry) were running for president that they were the most leftward senators, but that didn't reflect their voting record as a whole. Much depended on which votes you counted.
This year, according to VoteView the Senators farthest left in their view really were Warren, Harris, Booker, and Sanders. VoteView likely has biases of its own, but you can compare their rankings with those of other sites.
Different groups take different votes to evaluate politicians by so it could be that different organizations rate Biden further to the left and others more to the center of the Democratic pack...which of course is almost completely left of center.
True. If you count some votes in the current Congress the "squad" is the farthest left. Count other votes and it's other representatives like Maxine Waters.
With the "squad" and with Biden, the financial sector is very strong in their constituencies, so while the squad votes left on non-economic issues, when it comes to companies in their district they try to oblige the companies. If you don't have much of anything going on economically in your district it's easier to vote left when it comes to financial regulations.
Biden wanted to satisfy the corporations registered in Delaware. He also wasn't a real PC warrior back then, so it's unlikely that he was one of the most liberal Senators. With Bernie in the Senate, it wasn't likely that Biden - or even Obama - would be the most liberal.