This assumes that the rest of his party swings left, instead of right. Given that he chose the most right wing candidate possible for his VP, the fact that he's denounced the left multiple times during the debates, the fact that party leaders are all corporate shills, and given the fact that the democratic party has, on multiple occasions, done everything in their power to make sure that the democrats remain very, very right wing, I think it's extremely naive to think that anyone is going to push biden left. The democrats aren't leaning right because they're trying to appeal to moderate voters. They're leaning right, because the party leaders are right wing politicians themselves. They're hands aren't tied. They *want* to go further right.