Thanks for following our live coverage of the seventh debate of the Democratic primary season.

The debate in Iowa featured six of the remaining 12 candidates, and came just three weeks before Iowa voters go to the polls to select their Democratic candidate.

Progressive senators Elizabeth Warren and Bernie Sanders appeared to finally break what had been an informal truce, as they clashed over claims Sanders doubted the electablity of any female US presidential candidate.

Warren argued that she and the only other woman on stage - Amy Klobuchar - had a better track record of winning office than the men on stage, who she said had lost 10 elections between them.

Read the full time analysis from Anthony Zurcher in Iowa:

Bernie Sanders and Elizabeth Warren ramp up feud

Here's the most tweeted moments and candidates, according to Twitter's communications manager Nick Pacilio.

Perhaps unsurprisingly, Warren's sharp line about women being election winners came out on top.

Elizabeth Warren and Bernie Sanders - who clashed for the first time in recent days over a disputed story - appeared to end the night on a tense, frosty exchange.

They appeared to have a brief row, and didn't shake hands despite Sanders offering his to Warren.

Representatives of the Sanders campaign told the BBC's Anthony Zurcher that it was Warren who rejected the friendly gesture from Sanders.

Tom Steyer was standing beside the two leading progressives when it happened.

"I don't know what they were saying," Steyer told NBC afterwards.

"Whatever they were talking about I was trying to get out of the way as fast as possible."

The candidates are getting their fundraising emails out already.

The Sanders campaign said the debate helped to drive more than 15,000 donations within the first hour - the "single best fundraising hour of any debate so far".

Sanders was already leading the field in fundraising, hauling in $34.5 million in the fourth quarter of the last year. According to the campaign, donations were being made at a rate of 250 per minute

The Warren campaign emailed supporters to fund-raise off her line that female candidates outperformed men in 2018

A final tally of speaking time by the Washington Post shows Warren had the most, with 18.8 minutes, followed by Klobuchar and Sanders, and Steyer at the bottom with just 12.4 minutes.

Closing statements

Sanders is up, and highlights his key issues - healthcare, child care, criminal justice reform.

"How does it happen in this great country we are the only major nation not to guarantee health care to all? How does it happen we have a child care system that is dysfunctional, a criminal justice system which is broken and racist?"

"This is the moment when we have got to think big, not small. This is the moment when we have got to have the courage to take on the 1%, take on the greed and corruption of the corporate elite, and create an economy that will work for all of us."

Closing statements

Biden says "character is on the ballot this time around".

"The American character. Not what Donald Trump is spewing out: racism, xenophobia."

He says Americans must return to their "fundamental basic decency".

"We can overcome four years of Donald Trump. But eight years of Donald Trump would be a disaster and fundamentally change the United States of America."

Closing statements

Buttigieg echoed the message of unity instead of division put forward by fellow presidential hopefuls.

"If you are watching this at home, and you are exhausted by the spectacle of division and dysfunction, I'm asking you to join me to help turn the page on our politics.

"If you're a voter of colour feeling taken for granted by politics as usual, join me.

"If you're used to voting for the other party, but right now cannot look your kids in the eye to explain this president to them - join me."

Closing statements

"So much is broken in this country," begins Warren.

She says the disability community are undeserved, children are living in poverty, and gun violence is rampant - all issues that did not come up in today's over two-hour long debate.

"It comes to us to decide the future of this country," she says.

"Hope and courage. That is how I will make you proud everyday as your nominee and the first woman president of the United States of America."

Closing statements

"I played team sports my entire life," says Tom Steyer.

"The bond between teammates is deep and emotional and full of love. And as far as I'm concerned the American people are my teammates."

Republicans, led by President Trump, are "basically kicking the American people in the face," he adds.

"Together we can save the world," he says in closing.

Closing statements

The candidates are now offering their closing thoughts.

Klobuchar goes first.

"It is about your healthcare, it is about your schools," she says.

"I have won every race, every place, every time. I have gotten the highest voter turnout in the country when I've led the ticket. I have passed more bills as the lead Democrat than anyone who's in Congress that's running for president.

"If you are tired of the extremes in our politics, you have a home with me."

Image source, bbc

Just before the break, Biden was asked about Trump's relentless attacks on him and his family.

"I've been the object of his affections longer than anybody else on this stage," he said, laughing.

"I'm not worried about taking on Donald Trump at all," he said, adding that he was particularly excited to debate him on the economy if he won the Democratic nomination.

Working people "are being clobbered," Biden said. "They're being killed."

Image source, Getty Images

"Black voters who know me best support me," says Buttigieg when asked about his extremely low poll numbers among African Americans.

A recent Washington Post/Ipsos poll put Buttigieg's black support at 2% nationally. Biden leads among African-Americans with 48% support.

South Bend, Indiana - the city that Buttigieg led for eight years - is 62% white and 26% black according to the US census.

African-American voters are a key constituency for Democrats in both primary and general elections.

Although ballots in the first two contests of the year, Iowa and New Hampshire, will primarily be cast by white voters, the next contest in South Carolina will feature a majority black electorate.

Image source, Getty Images

Tom Steyer, the billionaire who has made climate change his signature issue, says he would issue a national emergency on climate on "day one" of his presidency.

The moderator asks him whether he is the best messenger for climate change, given the billions of dollars he made investing in fossil fuels.

"I divested from fossil fuels," he says. "I'll make it a priority. I have been doing it for some time."

Buttigieg says the US has to do more to reach out to Americans, such as energy sector workers, who feel that addressing climate change would be a "defeat for them".

"We need to enlist them in a national project," he says, adding that "equity and environmental justice has to be at the core".

Warren - who had made fighting corruption her marquee issue - says taking back the country from "corruption" in government is the only way to address climate issues.

Climate change: Where we are in seven charts

The candidates weigh in on the looming impeachment trial of President Trump.

"This is a decency check on our government," says Senator Klobuchar. "This is a patriotism check - not only this trial but this election."

Steyer says he is proud of spending millions to promote Trump's impeachment.

"Standing up for what's right is always worth it and I will never back down from that," Steyer says.

Warren, also a senator, is asked whether staying in DC for impeachment will be a problem on the campaign trail.

"I will be there because it is my responsibility," she says. "But that impeachment trial is going to show the American people .... the corruption of this administration. It's about Donald Trump putting Donald Trump first."

She says Democrats must be the party to fight on the side of the people.

BBC reporter Helier Cheung is at a DC debate watch party at local restaurant.

Nearly all the Democrats I spoke to at Busboys and Poets are still undecided between candidates.

Many were waiting to see what the interaction between Sanders and Warren would be like. When it came, Susanna Hogg, a 22-year-old aerospace engineer, described it as “about as tense as expected”.

She said she wasn't sure whether Sanders said it, but she said it was a “problematic opinion ... if he did say that I would take issue”.

Many younger Democrats suggested the TV debates were not the main way they would pick their candidate.

Hogg said she was the “kind of voter who won’t be totally decided until I’m at the ballot box”, while Phil Roberto, a 22 year old engineer, said he planned to do research and look at candidate outlines online to make his final decision.

Just before the halftime break, progressive Senator Elizabeth Warren said her proposed "wealth tax" would cover free college for all Americans.

Her plan calls for a 2% tax on those with more than $50m and 3% on those with more than $1bn.

Her plan has drawn many critics (including the entire Republican party and corporate CEOs), and especially among the American billionaire class. Microsoft CEO Bill Gates is among the critics of the plan, saying he would have been forced to pay far more tax.

Billionaire candidate Tom Steyer chimed in on stage that he too supported a wealth tax.

"The income inequality in this country is unbearable," said the former hedge fund manager.

Some Twitter users quickly called on him to donate his campaign funds to charity.

The BBC's Katty Kay notes that 74% of Americans support her plan. "That’s pretty astonishing. Americans agree on hardly anything but 74% agree on a 2% wealth tax," she wrote on Twitter.

Anthony Zurcher
BBC North America reporter

Growing tension between the two most liberal candidates, Elizabeth Warren and Bernie Sanders, has been the biggest news story in campaign politics in recent days.

Warren alleged that Sanders told her in December 2018 that a woman couldn’t win the presidency – something Sanders denied.

Sanders denied it again when asked about it during the debate. He has long supported the idea of a woman president, he said.

Then Warren had her turn in a set-piece response she clearly spent time crafting.

She started by implying that Sanders was lying, but quickly pivoted to pointing out the electoral success that she and Amy Klobuchar, the other female candidate on the stage, have had.

They’ve won every election they’ve been in, while the three male politicians onstage have lost 10 between them.

She ended by pitching herself as the unity candidate with a broad coalition.

"The real danger we face as Democrats is picking a candidate who can't pull party together or someone who takes for granted big parts of constituency," she said.

Given that Sanders has been criticised for being too divisive, Pete Buttigieg for not being able to draw significant minority support, and Biden for a lack of enthusiastic support, it was a roundhouse kick at the three candidates vying with her at the top of the polls.

We're now on the subject of schools. Biden is asked about universal infant care.

"I was a single parent too," Biden says, recounting the deaths of his wife and daughter in 1972, leaving him caring for his two young sons.

He says he'll expand funding for schools so that 3 to 5-year-olds will have full schooling and after school programmes.

He'll also have a tax credit to help put more women back to work, and will work to raise the salaries of caretakers, he says.

• The two hours costing US parents thousands

The candidates are benefitting from the slimmed-down field on the debate stage. A little over an hour into the debate, here are the speaking times for each candidate, according to a CBS News analysis.

By comparison, Sanders spoke for only 13:43 over the course of an entire evening during the debate in September last year, when ten candidates were on the stage.