A crisis of legitimacy swept across American politics in the second decade of the 21st century. Many people had the general conviction that the old order was corrupt and incompetent. There was an inchoate desire for some radical transformation. This mood swept the Republican Party in 2016 as Donald Trump eviscerated the G.O.P. establishment and it swept through the Democratic Party in 2020.

In the 2020 primary race Joe Biden stood as the candidate for linear change and Elizabeth Warren stood as the sharp break from the past. Biden was the front-runner, but fragile. Many of the strongest debate performers — Cory Booker, Amy Klobuchar, Pete Buttigieg and Michael Bennet — couldn’t get any traction because Biden occupied the moderate lane. By the time he faded, it was too late.

Warren triumphed over the other progressive populist, Bernie Sanders, because she had what he lacked — self-awareness. She could run a campaign that mitigated her weaknesses. He could not.

Biden was holding on until Warren took Iowa and New Hampshire. He or some other moderate could have recovered, but the California primary had been moved up to March 3, Super Tuesday. When Warren dominated most of the states that day, it was over. The calendar ensured that the most progressive candidate would win.