In 2016, the presidential election turned into a referendum against Hillary Clinton. In 2020, it might just become one against Donald Trump — that is, if the Democratic Party lets it.

Joe Biden had all but locked up the Democratic nomination prior to Sunday’s debate, but given the former vice president’s increasing penchant for gaffes and rhetorical fumbles, the two-person stage offered him the opportunity to undermine the case for his candidacy. Biden avoided this pitfall, in no small part due to Bernie Sanders.