A transformative President should have three things going for him/her:
1. Win big so you have a strong reservoir of legislative support and at least the perception of a mandate.
2. Know how to work the levers of political power so as to actually get large-scale legislation passed.
3. By dint of a unifying, popular persona and vision, bring the country along with you as change is implemented.
A plausible case can be made that Biden is well-positioned to do all three of these things. The non-ideological, non-insurgent nature of his candidacy, which infuriates so many on the left, should actually make it easier, not harder, to accomplish these goals. Just ask FDR.
Of course, you also need a big agenda with transformative potential. Biden has that as well, as a number of recent articles have documented. It is difficult to look at the list of ideas he is putting forward, with their associated price tags, and fault his campaign for a lack of ambition.
So will he be able to be such a President if he wins? An unequivocal maybe! But the potential is there and is greater than many think precisely because Biden is what he is: a non-ideological pragmatist.