Washington (AFP) - An ascendant Elizabeth Warren seized the spotlight and faced repeated attacks in Tuesday’s Democratic debate as Joe Biden often faded into the background, highlighting a shakeup in the 2020 nomination race.

The three-hour marathon saw Democrats largely unite against a common foil – President Donald Trump, whom many candidates said should be impeached – while expressing sharp disagreements over policy.

Here are four key questions following the debate.

- Is Warren the frontrunner? -

The progressive senator from Massachusetts last week finally drew even with former vice president Biden in polling, and her debate rivals unleashed a barrage of attacks as they gave Warren the frontrunner treatment for the first time.

Criticism piled up over her failure to explain how to pay for her ambitious plans and her lack of foreign policy credentials.

Ex-congressman Beto O’Rourke accused her of “being punitive” with her plan to tax the wealthy, while Senator Amy Klobuchar savaged Warren’s universal health care plan as a “pipe dream.”

“Simply because you have different ideas doesn’t mean you’re fighting for regular people,” Klobuchar said.

Warren parried most attacks and presented her counterargument that energizing disaffected Americans to vote rather than promote a return to “business as usual” is the best way to defeat Trump.

“The way we’re going to win is by addressing head-on what millions of Americans know in their bones, and that is that the wealthy and the well-connected have captured our democracy, and they’re making it work for themselves and leaving everyone else behind,” Warren said.

- Shrinking Biden? -

If Warren presented herself as the chief obstacle for anyone else seeking the nomination, Biden appeared as a less commanding presence, straying occasionally from the questions and offering some unsteady responses that generated little enthusiasm.

He was forceful in his critique of Warren on financial issues, and had a strong moment when he sold his advanced age and experience as an asset for the presidency. “With it comes wisdom,” the 76-year-old said.

But Biden failed to deliver a resounding blow against Trump when asked to address the president’s criticism of him and his son Hunter Biden over their involvement in Ukraine.

On Wednesday, Biden sounded unfazed by Warren’s rise, telling reporters in Ohio “it’s kind of about time other people get questioned.”

But he added that Warren ought to speak with more “candor” about her plans: “Tell us how you’re going to do what you say you’re going to do,” he said.

- Room for non-Biden moderates? -

Tuesday saw poise and previously unseen aggressiveness by Klobuchar and small-town mayor Pete Buttigieg, who were making the case for moderate alternatives to Biden.

Buttigieg, the first openly gay major US presidential candidate, launched his campaign with a bang but then failed to climb into the top tier. His fortunes could rise after a smart, strong performance.

The Indiana native went on the offensive, attacking Warren on health care, O’Rourke for seeking to seize private citizens’ guns, and fellow veteran Tulsi Gabbard for supporting Trump’s Syria troop withdrawal.

Throughout he appeared eager to prevent Democrats from shifting too far leftward in support of policies that may not play well in middle America, such as the Warren-backed universal health care proposal known as Medicare for All.

Klobuchar delivered a solid performance as another Midwest pragmatist who, while still progressive on social issues, suggested a “reality check” against Warren liberalism.

“I want to win those states that we lost last time, and I have bold ideas to get us there.”

- Bernie bouncing back? -

The grumpy darling of the far left suffered a mild heart attack this month, understandably raising questions about his health.

But he appeared energized onstage, joking with moderators and pronouncing himself healthy. “I’m feeling great,” he said, insisting he will be mounting a “vigorous campaign” over the coming months.

Polling numbers for Sanders have slumped and he trails Warren and Biden, but he remains a formidable force in the race, having outraised all rivals in the third quarter.

During the debate US media reported Sanders won the endorsement of popular congresswoman Alexandria Ocasio-Cortez and fellow liberals Ilhan Omar and Rashida Tlaib.

Sanders announced he is returning to the campaign trail with a major rally this weekend in New York.