Moderate Democratic presidential contenders pushed back against liberals on Tuesday as the second round of presidential debates opened with a fresh clash over the direction of the party.

Workers prepare the debate stage at the Fox Theater in Detroit, Michigan, on July 30, 2019, ahead of the 2nd Democratic Presidential Debate. (Photo: VCG)

Montana Gov. Steve Bullock demanded aggressive action on the nation's challenges but warned voters against nominating someone who embraces "wish-list economics" to take on President Donald Trump next year.

Working people "can't wait for a revolution," said Bullock in a clear swipe at self-described democratic socialist Bernie Sanders, who stood at center stage. "Their problems are here and now."

The warning from the little-known red-state governor came shortly before Sanders and progressive firebrand Elizabeth Warren promised to pursue bold liberal priorities if elected. The high-profile New England senators are known for their unapologetic embrace of aggressive plans to overhaul health care, higher education, child care and the economy — ambitious and expensive steps that may be popular among many Democrats but give Trump and his Republican allies ample opportunity to cast all Democrats as extreme.

"We're not going to solve the urgent problems we face with small ideas and spinelessness," Warren charged, calling for "a Democratic Party of big structural change."

The fight for the political left is just one subplot as the first wave of 10 candidates meets in Detroit. A second group of 10 that features early front-runner Joe Biden as well as Kamala Harris convenes Wednesday night. The groupings were chosen by debate host CNN at random.