The Democratic Party is ideologically broad, stretching from Vermont Sen. Bernie Sanders on the left to billionaire Michael Bloomberg on the right. The party is also demographically diverse, encompassing blacks, Latinos, Asians, urban white progressives, Midwestern working-class whites who are economically liberal but culturally conservative, the LGBTQ coalition, and more. Biden appealed to a much bigger share of the party than any other candidate in the primaries. That made him a formidable contender for the nomination and makes him a strong candidate to go up against Trump in November.

But that doesn’t mean Biden succeeds in being the perfect Democrat — with perfection defined as a candidate who manages to achieve maximal appeal to the members of the party’s highly differentiated electoral coalition. Obama, a once-in-a-generation political talent, may have come as close as possible to being such a perfect candidate during his 2008 presidential campaign. Today, the only person who approaches that level of support is imaginary — the “generic Democrat” pollsters ask voters about in their surveys…

A Biden who largely stays out of sight, avoiding embarrassing gaffes and steering clear of providing additional evidence of cognitive wear-and-tear, is a Biden who comes closer to resembling this imagined generic Democrat. The more he does the opposite, appearing frail and sounding flummoxed on a daily basis, the more his support is likely to sink, with imagined perfection slowly replaced in the minds of voters by all-too-real defects.