Surging US Democratic presidential contender Elizabeth Warren has come under repeated attack on her healthcare and tax policies in a debate as moderate rivals pushed her to explain how she would pay for ambitious proposals including her Medicare for All plan.
Warren's recent rise into a virtual tie with former vice-president Joe Biden in many opinion polls made her a frequent target for attacks that exposed the Democratic Party's divisions between its centrist and progressive wings on a range of issues.
The Democratic contenders for the White House were united, however, in supporting the Democratic-led impeachment inquiry of Republican President Donald Trump and criticising Trump's recent decision to withdraw from Syria.
Moderate rivals Pete Buttigieg, the mayor of South Bend, Indiana, and US Senator Amy Klobuchar, facing pressure to break out of the middle of the crowded Democratic presidential field, went after Warren on Tuesday for being evasive on her plan for universal healthcare and said her plan would mean higher taxes or Americans.
"I think we owe it to the American people to tell them where to send the invoice," Klobuchar told Warren.
Buttigieg chided Warren, who boasts she has a plan for everything, for not releasing a detailed healthcare plan with an explanation of how she would fund it.
The sharp exchanges were a sign of the heightened stakes as a dozen candidates crammed the debate stage in the electoral battleground state of Ohio.
It was the most crowded debate so far in the Democratic race to pick a challenger to Trump in the November 2020 election.
The debate comes at a critical time as Biden has seen his once solid lead in opinion polls in the Democratic race diminished by Warren, a leader of the party's progressive movement, who has steadily risen.
Warren stayed calm under the repeated attacks, offering her proposals to end income inequality and level the economic playing field for workers.
She did not directly respond to questions about whether she would raise taxes for the healthcare plan but she said she would not sign any bill that does not lower healthcare costs for middle-class families.
At the first debate since Democrats in Congress launched an impeachment probe against Trump, the candidates defended the inquiry and said the president needed to be held accountable for his actions and for stonewalling Congress on its probe.
The investigation focuses on Trump's efforts to pressure Ukraine to investigate his unsubstantiated allegation that Biden improperly tried to aid his son Hunter's business interests in Ukraine.
Biden and US Senator Bernie Sanders said Trump was "the most corrupt president in history" and Congress would be remiss if it did not pursue the impeachment probe.
"Impeachment is the way that we establish that this man will not be permitted to break the law over and over without consequences," Warren said.
Biden said Trump was going after him because he did not want to face him in November 2020.
"Look, my son did nothing wrong. I did nothing wrong. I carried out the policy of the United States government in rooting out corruption in Ukraine and that's what we should be focused on," Biden said.
"What I think is important is we focus on why it's so important to remove this man from office."
Most of the Democrats criticised Trump's abrupt decision to withdraw US troops from northern Syria, which cleared the way for a Turkish incursion to attack the Kurds, longtime US allies in the fight against Islamic State.
The debate marked the return of Sanders, 78, the oldest candidate in the field, who suffered a heart attack two weeks ago and has had stents inserted to open a blocked artery.