Democratic 2020 presidential candidate and senator Elizabeth Warren (D., Mass.) speaks during an event in Columbus, Ohio, May 10, 2019. (Maddie McGarvey/Reuters)

Elizabeth Warren enters the first Democratic debate tonight hoping to capitalize on some recent good headlines. She’s gained in polls, from an average of 6 percent in March to 12 percent today. Nate Silver observes that Warren’s rise has been at Bernie Sanders’s expense. Yesterday’s Moveon.org straw poll illustrates this trend. Warren was in sixth place in December, with 6 percent. Now, among progressive activists, she’s leading the field at 38 percent. Bernie is in second with 17 percent.


Warren’s good numbers have resulted in favorable press coverage. Not just the puff pieces about how she learned to “fight,” or about how “She has a plan for that.” I mean the articles that say Warren enjoys “momentum.” The trend began in May when The Hill ran a piece with the headline, “Warren shows signs of momentum after slow start.” “New Momentum for Elizabeth Warren,” says John Cassidy of The New Yorker. “Elizabeth Warren gains momentum in the 2020 race plan by plan,” says Lauren Gambino of the Guardian. “Warren’s momentum propels her up in our rankings,” CNN announced last week.

There’s a problem with using “momentum” as a criterion of analysis: It doesn’t exist. Or, at the very least, the phenomenon is exaggerated. In a recent paper, “Knockout Blows or the Status Quo? Momentum in the 2016 Primaries,” Vanderbilt University political scientists Joshua D. Clinton, Andrew M. Engelhardt, and Marc J. Trussler used a huge polling-data set to examine if primary victories affect support for candidates. “Preferences sometimes respond to election outcomes,” the authors conclude, “but the estimated effects are indistinguishable from effects occurring on nonelection days.”


Explaining his findings on Twitter, Trussler wrote, “So voters are learning and changing their opinions. But this learning is not primarily happening due to electoral wins and losses. It is happening every day on the campaign due to the regular patterns of surge/discovery/decline described so well by @johnmsides and @vavreck.”

If there’s little evidence for “momentum” after the voting begins, I’d suggest there’s even less reason to use the term to describe changes in polling months before the Iowa caucuses. Clearly, Elizabeth Warren is rising in national polls as Democratic primary voters abandon Bernie Sanders. But she has a long way to go — and must make inroads in groups other than white-collar liberals — before she can challenge Joe Biden’s frontrunner status. If she gets wrapped up in all the talk of momentum, she likely will end up disappointed.