How the average Joe (and Jane) could wind up stopping Warren

To win the nomination, Ms. Warren will need to advance beyond her factional base to a broader coalition. Historically, many left-liberal candidates have found it easy to attract 20-plus percent in the polls and five-digit crowds on the stump. Howard Dean (2004) and Bernie Sanders (2016) had done so by this point in the election cycle. But such candidates have found it far harder to win.

Those who manage to pull it off, like Barack Obama nationally or Bill de Blasio and Alexandria Ocasio-Cortez in New York City, often have special appeal to nonwhite voters. Without that advantage, they might have fallen short, as Zephyr Teachout and Cynthia Nixon did in New York State, or Jerry Brown and Gary Hart in presidential races.

There are important factors, which we’ll get to, that might make it easier today for a left-liberal candidate to win. The ranks of the activists have swelled in recent years, and Ms. Warren’s opposition could prove weak as well.

For now, it is not clear whether Ms. Warren has made the breakthrough.