The New York Times reports:

Diane Chojnowski and Denyce Rusch were among the Iowans who braved light snowfall and temperatures in the teens to see Senator Bernie Sanders on Sunday afternoon, a few hours before Senator Elizabeth Warren was also due in this liberal pillar of eastern Iowa.

But after Ms. Chojnowski and Ms. Rusch praised Mr. Sanders, they turned to a predicament far more bothersome than the winter weather: choosing between the two progressive candidates.

“You worry about Bernie and Elizabeth splitting the progressive vote because between the two of them they’ve got a huge bloc,” said Ms. Chojnowski, who initially considered Ms. Warren but has come back to Mr. Sanders because, as she put it, “he’s the thought leader.”

She is not the only liberal voter alarmed.

Since the presidential primary race began, the two senators — who have been friends since Ms. Warren was elected to the Senate in 2012 — have abided by a de facto nonaggression pact, rarely criticizing one another and frequently acting as something of a populist tag team on the debate stage. And as Pete Buttigieg has risen in the polls and Joseph R. Biden Jr. has proved durable, Mr. Sanders and Ms. Warren have been happy to demonstrate their left-wing bona fides by contrasting themselves with the more moderate contenders.

Yet with Mr. Sanders enjoying a revival after his heart attack in October and Ms. Warren receding from her summer surge but wielding a formidable political organization in the first nominating states, it’s increasingly clear that their biggest obstacle to winning the Democratic nomination is each other. [Continue reading…]