Washington (AFP) - At this week's Democratic presidential debates, Joe Biden withstood a barrage to maintain his frontrunner status, Elizabeth Warren captured the limelight with big imaginative proposals -- and deep ideological divides on America's political left were clear to see.

Twenty candidates clashed over two nights of contentious debate Tuesday and Wednesday. 

Too often, the contenders' focus appeared to be on dragging down one another and diving into the weeds on health care policy -- instead of on offering an uplifting vision for America or strategies to defeat President Donald Trump.

But while the Democrats grappled with their own frustrations about their party's divisions and its future, there were bright spots. 

Here are key takeaways from the Democrats' showdown in Detroit:

Biden better

Biden was more engaging, aggressive and on point Wednesday than he was in Miami last month. He needed to be in order to quiet murmurs that the 76-year-old former vice president was not up to the job.

He parried attacks from nearly every rival on stage, especially Senator Kamala Harris, whose criticism of Biden at the previous debate earned her a breakout moment.

When Harris clashed this time with Biden over health care, Biden punched back about what he claimed would be the exorbitant cost of her proposal.

"I don't know what math you do in California. But I tell ya, that's a lot of money," Biden said.

When Biden offered a forceful defense of his partnership with president Barack Obama, rivals hit him hard for his a la carte highlights of policies he liked, while remaining silent on those which appear outdated to the Democratic Party of 2019, such as increased deportations of immigrants.

"I guarantee you, if you're debating Donald Trump, he's not going to let you off the hook," New York mayor and longshot candidate Bill de Blasio advised Biden.

Warren in command

The popular senator from Massachusetts did well in the first debate on Tuesday, along with her chief liberal camp rival, fellow senator Bernie Sanders.

Warren offered lucid explanations of her many policies on health care, wages and immigration, and showed she was not afraid to urge Americans to dream big and call for dramatic change.

Moderate rivals, well aware of the risks of peddling overly progressive agendas on voters, challenged Warren on her "fairy tale economics," but Warren deftly pushed back.

"We are the Democrats," she said. "We are not about taking health care away from anyone and should stop using Republican talking points."

Second tier standouts, missteps

Senator Cory Booker has been patiently waiting for his star turn. It came Wednesday.

He turned in a sharp performance, outshining both Biden and Harris with doses of optimism, compassion, levity, and dead serious critique.

He hit several high notes: pointedly criticizing Biden over criminal justice policies he helped implement but is now scrambling to reverse; suggesting Democrats move beyond intraparty disagreements and unite against Trump; and showing empathy for voters in troubled cities like Detroit.

Former housing secretary Julian Castro, the only Latino in the race, also made a strong impression -- his second straight solid debate showing.

His shining moment came in a stern rebuke of Biden over immigration policy: "It looks like one of us has learned the lessons of the past and one of us hasn't."

Congresswoman Tulsi Gabbard delivered a confident performance, including a rock-solid argument for ending "regime change" wars and pouring that money into improving communities back home.

But some of the candidates underperformed, notably ex-congressman Beto O'Rourke, an early campaign standout, and Senator Amy Klobuchar, who was often on the periphery of Tuesday's discussion. 

Underwhelming message

During five hours of debate, Democrats focused more on dragging each other down than offering an aspirational message with which to challenge Trump.

The president's name was invoked, with some candidates openly branding him a "racist" who must be defeated next year.

But with many low-polling candidates realizing that July might be their final moment to make a national impression, the internal attacks dominated.

And the debate format -- 10 candidates per night, provocative questions pitting rivals against one another -- essentially forced the Democrats into swinging their sharp elbows.

Progressives repeatedly pressed their case for dramatic economic reforms, only giving ammunition to Trump's claim that Democrats are running on a "socialist" platform in 2020.