Sanders and Warren Battle Accusations of ‘Fairy Tale’ Promises as Center-Left Rift Flares

DETROIT — The leading liberal populists in the Democratic presidential primary, Senators Bernie Sanders and Elizabeth Warren, strenuously fought off accusations of impracticality and warnings of electoral ruin on Tuesday night, as a group of moderate underdogs sought to dent their momentum in the second round of presidential primary debates.

From the first moments onstage, there were charges of “wish-list economics” and critiques of “massive government expansions.” Gov. Steve Bullock of Montana, appearing in a debate for the first time, took implicit aim at Mr. Sanders by insisting that distressed farmers and teachers could not “wait for a revolution.” And former Representative John Delaney of Maryland conjured electoral catastrophes of the past to argue that the activist left could not be trusted to lead the party.

The course recommended by Mr. Sanders and Ms. Warren, Mr. Delaney said, was defined by “bad policies like ‘Medicare for All,’ free everything, and impossible promises that will turn off independent voters and get Trump re-elected.”

Mr. Sanders and Ms. Warren responded with defiance, rejecting the moderate candidates as offering policies that were plainly unequal to the political moment. Without taking aim at her more centrist rivals by name, Ms. Warren used her opening statement to dismiss their ethos of incremental change.

“We’re not going to solve the urgent problems that we face with small ideas and spinelessness,” Ms. Warren said.

Mr. Sanders, who has largely staked his candidacy on his support for single-payer health care, defended the policy ferociously, at one point accusing a CNN moderator, Jake Tapper, of using a “Republican talking point” when raising questions about his plan, and then noted that “the health care industry will be advertising tonight on this program.” Prompted to address Mr. Delaney’s criticism of “Medicare for All,” Mr. Sanders fired back laconically: “You’re wrong.”