Democratic White House front-runner Elizabeth Warren has found herself under fierce attack from her rivals in a live television debate.
Contenders accused the Massachusetts senator of dodging a question on whether she would raise taxes.
Twelve White House hopefuls squared off in the primetime forum, with two other front-runners also under pressure.
Joe Biden has been battling Republican personal attacks, while Bernie Sanders is recovering from a heart attack.
Tuesday night’s debate, hosted by CNN and the New York Times, in the electoral battleground state of Ohio was the most crowded so far in the Democratic race.
Also on stage were South Bend, Indiana, mayor Pete Buttigieg, California Senator Kamala Harris, New York entrepreneur Andrew Yang, former Texas congressman Beto O’Rourke, Minnesota Senator Amy Klobuchar, New Jersey Senator Cory Booker, former Obama housing secretary Julian Castro and Hawaii congresswoman Tulsi Gabbard and billionaire activist Tom Steyer.
Languishing on single digits in the opinion polls, they were striving to make a splash with time running out.
The Democratic White House race officially begins with the Iowa caucuses on 3 February.
The pack will be whittled down until a final candidate is crowned at the party convention next July, before he or she takes on President Donald Trump, a Republican, in the November 2020 election.
How did Warren find herself under attack?
Both Mr Sanders, a Vermont senator, and Ms Warren, a Massachusetts senator, favour an NHS-style system of free healthcare for Americans.
But unlike Mr Sanders, Ms Warren has repeatedly avoided stating explicitly whether her “Medicare for All” proposal would raise taxes on working families.
She was pressed on the issue by debate moderators and replied that she would not sign any bill that raises costs on the middle class.
Standing beside Ms Warren, Mr Buttigieg rounded on her, saying: “You heard it tonight, a yes or no question that didn’t get a yes or no answer.
“This is why people here in the Midwest are so frustrated with Washington in general and Capitol Hill in particular.
“Your signature, senator, is to have a plan for everything except this – no plan has been laid out to explain how a multi-trillion dollar hole in this Medicare for All plan that Senator Warren is putting forward is supposed to get filled in.”
Even Ms Warren’s progressive ally Mr Sanders took a veiled jab, saying: “I do think it is appropriate to acknowledge that taxes will go up.”
Senator Klobuchar pounced: “At least Bernie’s being honest here and saying how he’s going to pay for this and taxes are going to go up.
“And I am sorry, Elizabeth, but you have not said that, and I think we owe it to the American people to tell them where we are going to send the invoice.”
What did the candidates say about impeachment?
It was the first debate since congressional Democrats launched an impeachment inquiry into Mr Trump’s efforts to pressure Ukraine to investigate Joe Biden.
The first question of the night was about the congressional investigation that could attempt to remove the president from office.
In a show of unity, all candidates voiced support for the inquiry, railing against Mr Trump’s “criminality” and “corruption”.
What about the Hunter Biden story?
Mr Biden was asked about Mr Trump’s unsubstantiated claims that the former US vice-president improperly tried to aid his son Hunter Biden’s business interests in Ukraine.
“My son did nothing wrong,” he replied. “I did nothing wrong.”
“He [Mr Trump] doesn’t want me to be the candidate. He’s going after me because he knows that if I get the nomination I will beat him like a drum.”
When pressed by the debate moderator whether he made a mistake while he was the Obama administration’s point man on Ukraine by allowing his son to serve on the board of a Ukrainian gas company.
Mr Biden replied: “I never discussed a single thing with my son about anything having to do with Ukraine, no one has indicated I have. We’ve always kept everything separate.”
His Democratic rivals refrained from attacking Mr Biden on the issue.
How were the front-runners placed, going into the debate?
Mr Biden is aiming to steady his campaign after seeing his once commanding lead in opinion polls erode.
Mr Sanders is being closely watched in the three-hour debate for signs of flagging stamina after suffering a heart attack earlier this month.
The oldest contender at 78, Mr Sanders has dropped into third place in the polls.
Ms Warren was always expected to find a bullseye on her back on Tuesday night after accelerating to the tip of the field in the past two months.
Mr Biden recently jabbed at her “I have a plan for that” policy catchline, telling a New Hampshire crowd last week: “We’re not electing a planner.”
Mr Sanders, a progressive ally of Ms Warren, also took a swipe at her this past weekend.
“Elizabeth I think, as you know, has said that she is a capitalist through her bones. I’m not,” self-described democratic socialist Mr Sanders told ABC on Sunday.
Ms Warren has recently been under attack from Republicans about whether she was actually forced from her teaching job because of pregnancy half a century ago.
Critics have claimed there are inconsistencies in her story.
Ms Warren has previously apologised for a widely ridiculed claim of Native American heritage.
Who will take on Trump in 2020?
Election day is still more than a year away but the race to become the Democratic challenger to Mr Trump is already well under way.
Joe Biden and Bernie Sanders have thrown their hats into the ring, but most of the other candidates are relatively unknown outside the Washington DC bubble.
Find out more about the contenders.