Moderate frontrunner Joe Biden takes centre stage for the second leg of the Democratic presidential debates Wednesday after the first night exposed fault lines between the party's centrists and its progressive wing.
The former vice president - who is polling streaks ahead of his rivals for the nod to take on US President Donald Trump next year - is expected to come out re-energised and battle-ready after a lackluster debate performance last month.
Biden's opponents in Detroit include senators Kamala Harris and Cory Booker, the two most prominent candidates of colour, who are likely to seize on his 36-year Senate career to wrest the initiative.
Biden's record on crime and race - an issue that has engulfed Washington in the wake of sustained attacks by Trump on ethnic minority Democrats - are expected to come under the microscope.
The Pennsylvania native, whom Trump has dubbed Sleepy Joe, seemed unprepared and somewhat bewildered when Harris attacked him in June over his relations decades ago with segregationist senators.
"I'm not going to be as polite this time," Biden said at a fundraiser last week.
The debate features 20 candidates over two nights in Michigan, a battleground state Trump snatched in 2016.
Tuesday marked the most sustained assault yet by centrists on the bold platforms of leading progressives Bernie Sanders and Elizabeth Warren.
Warren warned that "spinelessness" over reform would perpetuate a "rigged system that has helped the wealthy and well-connected and kicked dirt in the faces of everyone else".
But she and Sanders faced dramatic pushback from ex-congressman John Delaney who delivered a scathing rebuke to their "fairy tale economics" that he said risked bankrupting the economy.
Sanders and Warren were peddling "bad policies like Medicare for All, free everything, and impossible promises that will turn off independent voters and get Trump re-elected", Delaney said.
The president himself was withering in his assessment of the evening, taking to Twitter to assert that only he could be trusted with the nation's finances.
"The people I saw on stage last night, & you can add in Sleepy Joe, Harris, & the rest, will lead us into an economic sinkhole the likes of which we have never seen before," Trump tweeted.
The stakes for this round of debates are sky-high, with the sprawling field of candidates likely to be winnowed by as much as half ahead of the next event in September.
Warren and Sanders - who are essentially tied for second, at about half Biden's support - have similar political platforms: Both back universal healthcare, tuition-free public college, tax hikes on the wealthy and aggressive Wall Street regulation.
They parried attacks throughout the two-and-a-half-hour debate that touched on everything from jobs and foreign policy to gun violence, taxes and how old is too old to be president.
"I don't care how old you are. I care about your vision," South Bend, Indiana Mayor Pete Buttigieg, 37, said of Sanders, the 77-year-old self-proclaimed "Democratic socialist" from Vermont.
But while Sanders called for a "political revolution", former Colorado governor John Hickenlooper cautioned against abolishing private health insurance for hundreds of millions of people.
Expanding healthcare ought to be "an evolution, not a revolution", Hickenlooper said.
Divisions also emerged on immigration and trade.
Warren's plan to decriminalise border crossings by undocumented migrants brought an animated response from Montana Governor Steve Bullock, who warned that would exacerbate problems.
"A sane immigration system needs a sane leader, and we can do that without decriminalising," he said.
With moderate rivals savaging ambitious but costly liberal policies, Warren lost her patience, coming up with the night's biggest applause line.
"I don't understand why anybody goes to all the trouble of running for president of the United States," she said, "to talk about what we really can't do and shouldn't fight for".
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