Biden main vulnerability at this point is within his own party, but in a different way than Clinton’s in 2016. Biden has shifted some of his policy positions to appease the left, but this move carries risks of losing moderates in his party. According to YouGov’s July 1 poll, a little over 25% of Democrats consider themselves “very liberal” ideologically; another 30% thought of themselves as merely “liberal,” while 42% consider themselves “moderate,” “conservative,” or “very conservative.” Interestingly, in that same July 1 poll, Biden showed some weakness most among the more moderate members of his party:

At the moment, Biden appears to have the support of over 90% of “liberal” and “very liberal” Democrats — moreover, virtually none of the defecting 10% say they would actually vote for Trump. By contrast, Biden is only at 81% among moderate and conservative Democrats, with 12% saying at this point they would vote for Trump. Surprisingly — given Biden’s moderate reputation during the primaries — the danger to him in November appears to come from center-right Democrats, rather than liberals.

Biden’s recent struggles among party moderates may be related to recent moves he has made to attract the Sanders-Warren wing of his party.