Ten Democrats have clashed in the first TV debate of the race to oust President Donald Trump from the White House.
Liberal firebrand Elizabeth Warren, who has been gaining momentum, took centre stage at the heated forum in Florida.
Candidates sparred over healthcare and immigration, and a couple of underdogs gulped much-needed political oxygen with a few well-timed zingers.
Ten other Democrats in the crowded field, including Joe Biden and Bernie Sanders, will battle on Thursday night.
Millions of voters were expected to tune in for America’s biggest political debates in years.
In Wednesday night’s two-hour debate in Miami, the candidates at times engaged in shouting matches as they vied to grab the limelight.
Ms Warren, a Massachusetts senator who has been surging in opinion polls, was one of only two contenders to say she supports replacing private medical insurance with government-run healthcare.
Taking aim at her rivals, Ms Warren drew loud applause as she said: “There are a lot of politicians who say, ‘oh, it’s just not possible’… what they’re really telling you is, they just won’t fight for it.”
“Well, healthcare is a basic human right and I will fight for basic human rights.”
Only New York Mayor Bill de Blasio backed her.
But Minnesota Senator Amy Klobuchar said: “I am just simply concerned about kicking half of America off of their health insurance in four years.”
Former US congressman John Delaney also warned against such a policy.
Beto O’Rourke, another ex-congressman, was first to show off his command of Spanish, saying that a stable democracy should “listen to all voices”.
But the one-time liberal golden boy found himself under heated attack from former Obama housing secretary Julian Castro, the only Latino in the race.
Mr Castro challenged Mr O’Rourke to support his plan to decriminalise illegal immigration, lecturing his fellow Texan to “do your homework”.
Two little-known candidates bickered over foreign policy, underscoring disunity among Democrats about overseas intervention.
Ohio congressman Tim Ryan insisted the US must stay “completely engaged” in the Middle East.
But Tulsi Gabbard, an anti-war Hawaii congresswoman, hit back: “Is that what you will tell the parents of those two soldiers who were just killed in Afghanistan?”
The studio audience also cheered Ms Warren as she delivered an impassioned soundbite on economic populism, looking to cement her surge in the opinion polls.
“Who is this economy really working for?” she said. “It’s doing great for a thinner and thinner slice at the top.”
Ms Warren, the only top-tier candidate on the stage, concluded: “We need to make structural change in our government, in our economy and in our country.”
New Jersey Senator Cory Booker was the only candidate who did not raise his hand when asked whether he would sign back on to the 2015 Iran nuclear deal as it was originally negotiated under the Obama administration.
When Washington state Governor Jay Inslee boasted of his record on reproductive rights, Ms Klobuchar drew applause for retorting: “There’s three women up here who have fought pretty hard for a woman’s right to choose.”
Mr Inslee recovered later when asked by a moderator what is the biggest geopolitical threat to the nation, and he replied to loud acclaim: “The biggest threat to the security of the United States is Donald Trump.”
Mr de Blasio distinguished himself on a question about gun violence, saying: “There’s something that sets me apart from all my colleagues running in this race and that is for the last 21 years I’ve been raising a black son in America.”
He said his son, Dante, has to use “special caution because there have been too many tragedies between our young men and our police”.
All the top 20 Democratic candidates need to demonstrate they have the electoral viability and political grit to defeat the Republican president.
But Mr Trump, who is running for a second term in office next year, seemed unimpressed as he watched the debate aboard Air Force One en route to Japan for a G20 summit.
He unleashed on the debate host, NBC, after it cut to a commercial break halfway through because of a glitch with the microphones.
His re-election campaign said the debate showed that Democrats were proposing “a radical government takeover of American society that would demolish the American Dream so many are gaining access to under the growing Trump economy”.
Two big beasts of the Democratic political jungle, Mr Biden and Mr Sanders, will offer competing visions for America on Thursday.
Front-runner Mr Biden, a former US vice-president making his third White House bid, is a pragmatic centrist who is regaining his footing after gaffes and about-turns.
Snapping at his heels is Mr Sanders, a Democratic socialist who is promising a “political revolution”, including free healthcare for all and paying off America’s $1.6tn (£1.25tn) student debt mountain.
Youthful mayor Pete Buttigieg, whose dark horse campaign has been rocked by the police shooting of a black man in his home city of South Bend, Indiana, will be closely watched, too.
Senator Kamala Harris, the only black woman in the race; Senator Kirsten Gillibrand, who has campaigned on women’s issues; and entrepreneur Andrew Yang will also jockey for attention.
The line-up for both nights was chosen at random by NBC.
The eventual Democratic White House nominee will be crowned at the party convention in July next year, before the presidential election in November.