Hillary Clinton and Bernie Sanders aggressively challenged each other's fitness to be president in a Democratic debate, with the vital New York primary just days away.
They wrangled over Wall Street banks, the minimum wage and gun control at a pivotal moment in the campaign, with Mrs Clinton leading in the delegate count but Mr Sanders generating huge enthusiasm for his candidacy.
Mrs Clinton has accumulated 1,289 pledged delegates from primaries and caucuses while Mr Sanders has 1,038.
Her lead grows significantly when the superdelegates are added in - 1,758 for Mrs Clinton and 1,069 for Mr Sanders.
It takes 2,383 to clinch the Democratic nomination, and Mr Sanders needs to win 68% of the remaining delegates and uncommitted superdelegates to reach that figure.
The Vermont senator took a biting and often sarcastic tone as he sought to chip away at Mrs Clinton's credibility at the televised Brooklyn event.
He cited her support for the unpopular Iraq war and for free trade agreements, as well as her willingness to accept money through a super political action committee, as evidence that she lacks the judgment to lead the nation.
Mrs Clinton said Mr Sanders was unprepared to implement even his signature policy proposals, including breaking up big banks.
"I think you need to have the judgment on day one to be commander in chief," she said.
The debate was the first for the Democratic candidates in five weeks. It came ahead of Tuesday's primary in New York, a high-stakes contest with a huge cache of delegates at stake.
For Mrs Clinton, a win in her adopted home state would blunt Mr Sanders' recent momentum and put his pursuit of the nomination further out of reach.
But an upset for Mr Sanders would shake up the race, raising fresh concerns about Mrs Clinton's candidacy and breathing new life into his campaign.
Mr Sanders has accused Mrs Clinton of being part of a rigged economic and political system, hammering her repeatedly for giving paid speeches to Wall Street banks and refusing to release the transcripts.
Mrs Clinton continued to struggle to explain why she has not released the transcripts, saying only that she will do so when other candidates are required to do the same thing.
She tried to raise questions about Mr Sanders' own openness for not releasing his income taxes.
The senator pledged to release his most recent tax returns on Friday, and said there would be "no big money from speeches, no major investments" in the disclosures.
Mr Sanders has won a string of recent primary contests, including a big victory earlier this month in Wisconsin.
But because Democrats award their delegates proportionally, he has struggled to cut into the lead Mrs Clinton took earlier in the voting.
He has also failed to persuade superdelegates - the party insiders who can back the candidate of their choice regardless of how their states vote - to switch their loyalties from Mrs Clinton.
Despite his long mathematical odds, Mr Sanders has vowed to stay in the race through the party's convention in July. Backed by legions of loyal supporters, he has amassed impressive fundraising totals that give him the financial clout to do just that.