Biden has a long history being in the Senate. Since he's from Delaware, he's had a hand in propping up financial institutions and supporting legislation that has made it harder for middle and working class people.
His comments on busing, the Anita Hill saga, the crime bill... are all fair game.
With that said, if he's the nominee, of course you should vote for him over the orange idiot. But with this Dem primary, as a voter who sees our new Guilded Age, I'm looking for someone looking to do big shid and shake things up to improve our lives. The fact that Warren is running and has been on the right side of history regarding consumer protections in direct throw against Biden should scare the hell out of him.