WATCH LIVE: Democrats face off in first debate of 2016

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All eyes are on Hillary Clinton and Bernie Sanders as they take the stage in Charleston, S.C., Sunday for the NBC News/YouTube debate and political insiders expect to see some of the biggest fireworks between those two candidates.

Sanders released details of his highly-anticipated "Medicare-for-all" universal healthcare plan late Sunday, just hours before the debate, including how he would pay for it.

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The debate marks the last face-to-face encounter until Iowa kicks off the presidential nominating race in two weeks, and will also include Martin O'Malley, who is polling far behind Sanders and Clinton.

Clinton's campaign took aim at Sanders last week over his healthcare plan, saying the U.S. senator from Vermont had not said how he plans to pay for it.

Check out images from the last debate:

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12/19/2015: Third Democratic Debate
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WATCH LIVE: Democrats face off in first debate of 2016
MANCHESTER, NH - DECEMBER 19: Democratic president candidate Bernie Sanders takes the stage at the democratic debate at Saint Anselm College December 19, 2015 in Manchester, New Hampshire. This is the third Democratic debate featuring Democratic candidates Hillary Clinton, Bernie Sanders and Martin O'Malley. (Photo by Andrew Burton/Getty Images)
Hillary Clinton, former Secretary of State and 2016 Democratic presidential candidate, waves as she arrives to the Democratic presidential candidate debate at Saint Anselm College in Manchester, New Hampshire, U.S., on Saturday, Dec. 19, 2015. A Democratic presidential campaign that has looked tame compared to the one being waged by Republicans appears to be taking a sharp turn for the nasty as the three candidates participate in their third debate. Photographer: Andrew Harrer/Bloomberg via Getty Images
US Democratic Presidential hopefuls (L-R) Bernie Sanders, Hillary Clinton and Martin O'Malley participate in the Democratic Presidential Debate hosted by ABC News at Saint Anselm College in Manchester, New Hampshire, on December 19, 2015. AFP PHOTO / JEWEL SAMAD / AFP / JEWEL SAMAD (Photo credit should read JEWEL SAMAD/AFP/Getty Images)
Bernie Sanders, left, Hillary Clinton, center, and Martin OâMalley, right, participate in a Democratic presidential primary debate Saturday, Dec. 19, 2015, at Saint Anselm College in Manchester, N.H. At the table are debate moderators Martha Raddatz, left, and David Muir, of ABC News. (AP Photo/Jim Cole)
Martin OâMalley, right, speaks alongside Bernie Sanders, left, and Hillary Clinton, center, during a Democratic presidential primary debate Saturday, Dec. 19, 2015, at Saint Anselm College in Manchester, N.H. (AP Photo/Jim Cole)
Bernie Sanders speaks during a Democratic presidential primary debate Saturday, Dec. 19, 2015, at Saint Anselm College in Manchester, N.H. (AP Photo/Jim Cole)
US Democratic Presidential hopefuls (L-R) Bernie Sanders, Hillary Clinton and Martin O'Malley participate in the Democratic Presidential Debate hosted by ABC News at Saint Anselm College in Manchester, New Hampshire, on December 19, 2015. AFP PHOTO / JEWEL SAMAD / AFP / JEWEL SAMAD (Photo credit should read JEWEL SAMAD/AFP/Getty Images)
Bernie Sanders, left, offers an apology to Hillary Clinton during a Democratic presidential primary debate Saturday, Dec. 19, 2015, at Saint Anselm College in Manchester, N.H. (AP Photo/Jim Cole)
Senator Bernie Sanders, an independent from Vermont and 2016 Democratic presidential candidate, arrives to the Democratic presidential candidate debate at Saint Anselm College in Manchester, New Hampshire, U.S., on Saturday, Dec. 19, 2015. A Democratic presidential campaign that has looked tame compared to the one being waged by Republicans appears to be taking a sharp turn for the nasty as the three candidates participate in their third debate. Photographer: Andrew Harrer/Bloomberg via Getty Images
US Democratic Presidential hopefuls (L-R) Bernie Sanders, Hillary Clinton and Martin O'Malley participate in the Democratic Presidential Debate hosted by ABC News at Saint Anselm College in Manchester, New Hampshire, on December 19, 2015. AFP PHOTO / JEWEL SAMAD / AFP / JEWEL SAMAD (Photo credit should read JEWEL SAMAD/AFP/Getty Images)
Senator Bernie Sanders, an independent from Vermont and 2016 Democratic presidential candidate, speaks during the Democratic presidential candidate debate at Saint Anselm College in Manchester, New Hampshire, U.S., on Saturday, Dec. 19, 2015. A Democratic presidential campaign that has looked tame compared to the one being waged by Republicans appears to be taking a sharp turn for the nasty as the three candidates participate in their third debate. Photographer: Andrew Harrer/Bloomberg via Getty Images
Hillary Clinton speaks during a Democratic presidential primary debate Saturday, Dec. 19, 2015, at Saint Anselm College in Manchester, N.H. (AP Photo/Jim Cole)
Hillary Clinton, former Secretary of State and 2016 Democratic presidential candidate, smiles after walking on stage following a break in the Democratic presidential candidate debate at Saint Anselm College in Manchester, New Hampshire, U.S., on Saturday, Dec. 19, 2015. A Democratic presidential campaign that has looked tame compared to the one being waged by Republicans appears to be taking a sharp turn for the nasty as the three candidates participate in their third debate. Photographer: Andrew Harrer/Bloomberg via Getty Images
Senator Bernie Sanders, an independent from Vermont and 2016 Democratic presidential candidate, left, and Hillary Clinton, former Secretary of State and 2016 Democratic presidential candidate, share a laugh during a break in the Democratic presidential candidate debate at Saint Anselm College in Manchester, New Hampshire, U.S., on Saturday, Dec. 19, 2015. A Democratic presidential campaign that has looked tame compared to the one being waged by Republicans appears to be taking a sharp turn for the nasty as the three candidates participate in their third debate. Photographer: Andrew Harrer/Bloomberg via Getty Images
Senator Bernie Sanders, an independent from Vermont and 2016 Democratic presidential candidate, left, and Hillary Clinton, former Secretary of State and 2016 Democratic presidential candidate, share a laugh during a break in the Democratic presidential candidate debate at Saint Anselm College in Manchester, New Hampshire, U.S., on Saturday, Dec. 19, 2015. A Democratic presidential campaign that has looked tame compared to the one being waged by Republicans appears to be taking a sharp turn for the nasty as the three candidates participate in their third debate. Photographer: Andrew Harrer/Bloomberg via Getty Images
MANCHESTER, NH - DECEMBER 19: Democratic president candidate Bernie Sanders waits as Hillary Clinton walks on stage at Saint Anselm College December 19, 2015 in Manchester, New Hampshire. This is the third Democratic debate featuring Democratic candidates Hillary Clinton, Bernie Sanders and Martin O'Malley. (Photo by Andrew Burton/Getty Images)
MANCHESTER, NH - DECEMBER 19: Democratic president candidate Bernie Sanders speaks at the debate at Saint Anselm College December 19, 2015 in Manchester, New Hampshire. This is the third Democratic debate featuring Democratic candidates Hillary Clinton, Bernie Sanders and Martin O'Malley. (Photo by Andrew Burton/Getty Images)
2016 Democratic presidential candidates Senator Bernie Sanders, an independent from Vermont, from left, Hillary Clinton, former Secretary of State, and Martin O'Malley, former governor of Maryland, participate in the Democratic presidential candidate debate at Saint Anselm College in Manchester, New Hampshire, U.S., on Saturday, Dec. 19, 2015. A Democratic presidential campaign that has looked tame compared to the one being waged by Republicans appears to be taking a sharp turn for the nasty as the three candidates participate in their third debate. Photographer: Andrew Harrer/Bloomberg via Getty Images
Martin O'Malley, former governor of Maryland and 2016 Democratic presidential candidate, speaks during the Democratic presidential candidate debate at Saint Anselm College in Manchester, New Hampshire, U.S., on Saturday, Dec. 19, 2015. A Democratic presidential campaign that has looked tame compared to the one being waged by Republicans appears to be taking a sharp turn for the nasty as the three candidates participate in their third debate. Photographer: Andrew Harrer/Bloomberg via Getty Images
Martin O'Malley, former governor of Maryland and 2016 Democratic presidential candidate, right, speaks as Hillary Clinton, former Secretary of State and 2016 Democratic presidential candidate, listens during the Democratic presidential candidate debate at Saint Anselm College in Manchester, New Hampshire, U.S., on Saturday, Dec. 19, 2015. A Democratic presidential campaign that has looked tame compared to the one being waged by Republicans appears to be taking a sharp turn for the nasty as the three candidates participate in their third debate. Photographer: Andrew Harrer/Bloomberg via Getty Images
US Democratic presidential hopeful Hillary Clinton smiles as she walks past fellow candidate Bernie Sanders during a break of the Democratic Presidential Debate hosted by ABC News at the Saint Anselm College in Manchester, New Hampshire, on December 19, 2015. AFP PHOTO/JEWEL SAMAD / AFP / JEWEL SAMAD (Photo credit should read JEWEL SAMAD/AFP/Getty Images)
Hillary Clinton speaks during a Democratic presidential primary debate Saturday, Dec. 19, 2015, at Saint Anselm College in Manchester, N.H. (AP Photo/Jim Cole)
Martin OâMalley speaks during a Democratic presidential primary debate Saturday, Dec. 19, 2015, at Saint Anselm College in Manchester, N.H. (AP Photo/Jim Cole)
Bernie Sanders speaks during a Democratic presidential primary debate Saturday, Dec. 19, 2015, at Saint Anselm College in Manchester, N.H. (AP Photo/Jim Cole)
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According to Sanders' plan, individuals would pay a 2.2 percent "premium" and employers would pay a 6.2 percent payroll tax to fund the healthcare plan. Individuals making $250,000 to $500,000 a year would pay a tax rate of 37 percent and those making more than $10 million would pay a 52 percent tax rate.

Clinton is expected to also hit Sanders aggressively over his position on gun control, which is softer than many other Democrats. The debate venue is very close to the Emanuel AME church where Dylann Roof shot and killed nine black parishioners this past summer.

SEE ALSO: Tightening Clinton-Sanders battle raises stakes for Democratic debate

The debate, which will be broadcast on NBC News and streamed on YouTube in addition to right here on AOL.com, is hosted by the Congressional Black Caucus Institute.

(Reporting AOL.com with additional reporting for Reuters by Amanda Becker; Reuters editing by Jonathan Oatis)

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