LOS ANGELES — The Democratic Party's shrinking 2020 class clashed over the defining issue for their party’s primary voters — electability — as they met on the debate stage Thursday for the sixth and final time in 2019.

The face-off among the seven Democratic candidates was substantive and civil early on, lacking any sign of the political tumult that dominated Washington the day before as the House voted to impeach President Donald Trump. But just a month and a half before voting begins in Iowa, the stakes were high.

Massachusetts Sen. Elizabeth Warren, her momentum in the race stalled, appeared to slap her party’s centrist rivals as she made the case that her push to transform the nation’s political and economic system would defeat Trump next fall. She argued that prosecuting the case against the president would require a presidential nominee who can draw a sharp distinction between “the corruption of the Trump administration” while fighting “not for the wealthy and well connected” but for “everyone else.”

The specific arguments may be evolving, but the broader questions looming over the Democratic Party’s 2020 nomination fight have not: Democrats are not close to unifying behind a message or messenger in their quest to deny Trump a second term.

In fact, as Thursday’s debate hinted at, the party is still consumed by a high-stakes tug-of-war between feuding factions that must ultimately come together to beat Trump next November. One side, led by Warren and Vermont Sen. Bernie Sanders, is demanding transformational change to the U.S. economy and political system. The other, led by former Vice President Joe Biden and South Bend, Indiana, Mayor Buttigieg, prefers a more cautious return to normalcy after Trump’s turbulent reign.

Weighing in on the ideological fight, billionaire activist Tom Steyer dinged Buttigieg for not having a more aggressive plan to combat climate change.

“I would call on Mayor Buttigieg to prioritize this higher,” Steyer charged.

“We have to summon the energies of the entire country to deal with this,” Buttigieg responded. “I’ve seen politicians in Washington saying the right things on climate change as long as I’ve been alive.”

Amid the ideological fight, Democrats faced a pointed challenge directly related to their need to build a diverse coalition to win the general election. For the first time this primary season, no black or Latino candidate appeared onstage.

The omission was embarrassing, at best -- and politically dangerous, at worst -- as Democrats fight to convince people of color that they’re not taking their vote for granted.

Asked what message the lack of diversity on the debate stage sends, Sanders tried to shift back to the previous discussion about climate change.

Admonished by one of the moderators to stick to the question, Sanders countered that people of color will suffer “the most if we do not deal with climate change.”

The only nonwhite candidate on stage, Andrew Yang, called it “both an honor and a disappointment” to be the only candidate of color on the debate stage. He said he missed California Sen. Kamala Harris, who folded her campaign this month, and New Jersey Sen. Cory Booker, who failed to qualify. “I think Cory will be back,” Yang predicted.

Despite the potential for intraparty discord, the early moments of Thursday’s debate offered only mild distinctions between Democrats who, above all, share criticism of the Republican president’s vision for America.

“The president is not king in America,” said Minnesota Sen. Amy Klobuchar, who is preparing to serve as a juror at Trump’s impeachment trial in the Senate. Alluding to former President Richard Nixon, she added, “If the president claims that he is so innocent, then why doesn’t he have all the president’s men testify?”

Biden knocked Trump’s argument that less than half of Americans support his removal from office.

“He’s dumbing down the presidency beyond what I even thought he would do,” Biden said. “We need to restore the integrity of the presidency.”

The candidates also railed against Trump’s economy, despite outward indicators that the economy is doing well.

The U.S. unemployment rate stands at a half-century low of 3.5%, backed by consistently strong job gains in recent months that have largely squelched fears of a recession that had taken hold over the summer.