Hillary Clinton Hillary Diane Rodham ClintonHillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters FBI chief says Russia is trying to interfere in election to undermine Biden MORE and Bernie Sanders Bernie SandersMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters Why Democrats must confront extreme left wing incitement to violence MORE traded vigorous verbal blows in the last Democratic debate before the Iowa caucuses and New Hampshire primary on Sunday evening, both showing a clear understanding that the stakes could hardly be higher.

The two front-runners traded wonky digs at each other’s platforms as well as more personal attacks in a debate reflective of the heightened rhetoric that has been heard on the trail during the past week.

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Clinton, who has seen her lead shrink in Iowa in recent weeks, emphasized her closeness to President Obama and cast Sanders as much less stalwart in his support for the president.

That could be an effective gambit, esspecially in the state where the debate was held — South Carolina — where Obama is extremely popular with the black voters who make up a substantial part of the Democratic primary electorate.

But Sanders hit back hard at Clinton on issues including her links to Wall Street and what he called her embrace of "a Republican criticism" of his healthcare plan.

For all the heat of their exchanges, however, it was hard to point to a game-changing moment or even a clear victor.

Rather, the clash underscored the differences between Clinton's view that she is proven and tested, and Sanders's counter-argument that only he can bring the dramatic changes he believes the nation needs.

The debate was lively from its opening moments but it grew especially contentious when the candidates sparred over Wall Street.

"I don't get personal speaking fees from Goldman Sachs," Sanders said, dropping one of the night's main zingers.

Several minutes later, he came back to the topic again, telling Clinton: "You've received over $600,000 in speaking fees from Goldman Sachs.”

Seemingly prepared for the attack, Clinton pushed back, slapping Sanders for the Vermont senator's criticism of President Obama's relationships with Wall Street and the donations he accepted from wealthy bankers.

"I'm going to defend Dodd Frank and I'm going to defend President Obama," she said.

"Your profusion of your comments about your feelings towards President Obama are a little strange considering what you said about him in 2011," Clinton added, a reference to a period during which Sanders said a primary challenge to Obama would be a "good idea."

But Sanders insisted that he and Obama are "friends" with "some differences of opinion,” and questioned Clinton’s commitment to Wall Street reform.

"Can you really reform Wall Street when they are spending millions and millions of dollars on campaign contributions and providing speaking fees to individuals?" he asked.

"I have doubts when people receive huge amounts of money from Wall Street.”

The Sunday night debate hosted by NBC News and YouTube came ahead of Monday's Martin Luther King Jr. holiday, and in the middle of what is, for many people, a three-day weekend. That timing has been part of the criticism leveled against the Democratic National Committee. Clinton opponents have accused the DNC of stacking the deck for her by scheduling debates at times when they are unlikely to draw huge audiences.

The Democratic primary between Clinton and Sanders had been relatively uneventful until recent weeks when polls tightened, especially in Iowa, where Clinton had held a comfortable lead. The Clinton campaign has become more aggressive in response, haunted by the memories of 2008 when then-Sen. Barack Obama (D-Ill.) defeated Clinton in the primary despite her being a prohibitive favorite early on.

Clinton's campaign attacked Sanders from the right on health care last week, including suggesting his proposal for a universal plan had not been properly costed. A Sanders aide swatted away those jabs, describing the attacks as "Karl Rove tactics.”

The candidates deepened that divide on health care on the stage, hours after Sanders released the details of his "Medicare for all" plan.

Clinton framed her argument in terms of the scale of the achievement — from a Democratic perspective — of the Affordable Care Act. She questioned whether the country at large, or the Democratic Party, had the appetite for another huge fight over healthcare.

“We've accomplished so much,” she said. “I do not want to see Republicans repeal it and I do not want us to start over with a contentious debate. I want us to defend and build on the Affordable Care Act and improve it."

But Sanders described some of the broader attacks from the Clinton campaign on his health plan as “nonsense,” noting that its whole thrust is about trying to extend insurance to the tens of millions of Americans without health insurance.

Still he acknowledged that his new, hours old, plan was "not all that detailed,” when NBC News co-moderator Andrea Mitchell pressed him on it.

Right off the bat, moderators challenged Sanders on gun control, an issue that's dogged him as Democrats continue to shift to the left on the issue. Clinton ran down a list of pro-gun rights stances he's taken in Congress and noted that she was pleased that he "reversed his position" on legislation that provided the gun industry with immunity from certain civil lawsuits.

Moderators also forced Sanders the fact that he polls poorly with minorities — and at a debate co-sponsored by the Congressional Black Caucus Institute. Despite being within striking distance of Clinton in the lily-white states of Iowa and New Hampshire, he faces much deeper holes in Nevada and South Carolina, two early voting states with more diverse populations.

Sanders cast doubt on polling in general, noting the dramatic change since he entered the race miles behind a seemingly-insurmountable Clinton lead.

“When the African-American community becomes familiar with my Congressional record and with my agenda and my views on the economy and criminal justice, just as the general population has become more supportive, so will the African-American community and the Latino community," he said.

"We have the momentum, we are on a path to victory.”

Republican National Committee chairman Reince Priebus said this week he'd rather his party’s nominee face Clinton, the RNC spent Sunday night sending out multiple releases buoying Sanders' points, including one at the end trumpeting a "Sanders 'blowout.'"

Martin O’Malley, the former Maryland governor who just made the polling threshold to participate in the event, often struggled for speaking time amid the more robust disagreements between Sanders and Clinton.

When he did get time to speak, he worked to cast himself as both the youthful and more consistently progressive alternative to the two polling leaders. But he often struggled for speaking time in between the more robust disagreements between Clinton and Sanders.