With the debate stage narrowed to less than ten candidates for the first time, tensions flared as the top Democrats went toe-to-toe 46 days from the Iowa caucuses.

The big picture: Following the House's historic vote Wednesday night, the debate predictably opened with a question about impeaching President Trump — a moment that was quickly overshadowed as the candidates moved on to campaign finance, electability and experience, health care and more.

Highlights

1. Impeachment: With Rep. Tulsi Gabbard, who voted "present" on impeachment last night, failing to qualify for the sixth debate, the candidates were united in their condemnation of Trump's conduct. Where they differed was their characterization of the problem.

Joe Biden cast the Ukraine scandal as an embodiment of Trump's personal flaws and the threat he poses to the country, while Sens. Bernie Sanders and Elizabeth Warren highlighted the systemic corruption that allowed Trump to assume the presidency in the first place.

Andrew Yang called for looking past impeachment and focusing on addressing the "real problems" that propelled Trump's election: economic upheaval driven by job loss and automation.

2. Pile on Pete: Buttigieg faced a series of attacks as tensions that had been brewing on the campaign trail broke out on the debate stage — most notably during a heated exchange with Warren over campaign fundraising.

Warren attacked the South Bend mayor for hosting a high-dollar fundraiser in a Napa Valley wine cave: "Think about who comes to that," Warren argued, decrying the influence of money in politics and the corruption of decisions made in "smoke-filled rooms."

Buttigieg countered that it would be self-destructive to turn down donations from anyone while engaged in "the fight of our lives" against Trump, before pointing out that Warren and other successful Democrats used the same tactics before Warren swore off high-dollar fundraisers this year: "This is the problem with issuing purity tests you cannot pass yourself," he argued.

3. Moderates v. moderates: Sen. Amy Klobuchar had her strongest debate performance yet, but instead of hitting progressives Sanders and Warren, she took aim at the only other Midwestern moderate on stage. Set to embark on a 27-county bus tour of Iowa, Klobuchar ripped into Buttigieg for his lack of experience and failure to win elections outside of South Bend as she looked to chip into the mayor's advantage in the early state.

4. Yang shines: Andrew Yang called it both "an honor and a disappointment" that he was the only candidate of color on stage, before pivoting to his stump speech by rattling off statistics that explain the economic disadvantages that minorities face: "Fewer than 5% of Americans donate to political campaigns. You know what you need to donate to political campaigns? Disposable income."

Yang deftly parried questions into answers that reflect his core campaign themes and "Freedom Dividend" proposal, as he got more camera time in front of voters on a winnowed stage.

The bottom line: The relentless attacks on Buttigieg could shake up the race. But it's worth remembering that anything that doesn't alter the fundamentals of the campaign benefits the frontrunner. That remains Joe Biden, who slipped through tonight unscathed and with a stronger command of his answers than in prior debates.

Go deeper: An issue-by-issue recap of the Democratic debate