Let’s put it another way, every single factor that caused reluctant Republicans to hold their noses and vote for Trump will apply to reluctant Democrats. “Binary choice,” they’ll hear. “Judges,” they’ll declare. And, unlike 2016, when a host of people on both sides of the aisle thought there was no way that Hillary Clinton would lose to Donald Trump, not a single member of the Democratic coalition will be complacent. They’ll attack the election with fierce moral urgency. In other words, don’t hold your breath waiting for a “Never Bernie” movement in progressive media.
Next, when considering the effect of negative polarization, never forget that Team Blue is simply bigger than Team Red. Republicans have one exactly one popular vote since 1988, and they won that (in 2004) by a mere 2.4 points.
The difference is particularly staggering if you look at voting peaks. Donald Trump won 62,984,828 votes in 2016, more than any GOP candidate in history. In 2008—when America had a smaller population—Barack Obama won 69,498,516. Bernie Sanders is no Barack Obama, but the Democrats have a higher floor, and a higher ceiling.
Yes, I know all about the Electoral College, but to give you a sense of the fragility of Trump’s lead, just remember that two of his states—Wisconsin and Michigan—would be blue if Hillary had been able to generate Obama’s 2012 turnout in just two cities, Milwaukee and Detroit.