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- LAS VEGAS, NV - OCTOBER 13: (L-R) Democratic presidential candidates U.S. Sen. Bernie Sanders (I-VT), Hillary Clinton and Martin O'Malley take part in a presidential debate sponsored by CNN and Facebook at Wynn Las Vegas on October 13, 2015 in Las Vegas, Nevada. Five Democratic presidential candidates are participating in the party's first presidential debate. (Photo by Joe Raedle/Getty Images)
- Martin O'Malley, former governor of Maryland, participates in the first Democratic presidential debate at the Wynn Las Vegas resort and casino in Las Vegas, Nevada, U.S., on Tuesday, Oct. 13, 2015. While tonight's first Democratic presidential debate will probably lack the name-calling and sharp jabs of the Republican face-offs, there's still potential for strong disagreements between the party's leading contenders. Photographer: Josh Haner/Pool via Bloomberg
- LAS VEGAS, NV - OCTOBER 13: Democratic presidential candidates (L-R) Hillary Clinton, Martin O'Malley and Lincoln Chafee take the stage for a presidential debate sponsored by CNN and Facebook at Wynn Las Vegas on October 13, 2015 in Las Vegas, Nevada. The candidates participated in the party's first presidential debate with Jim Webb and Sen. Bernie Sanders (I-VT). (Photo by Alex Wong/Getty Images)
- LAS VEGAS, NV - OCTOBER 13: (L-R) Democratic presidential candidates Jim Webb, Sen. Bernie Sanders (I-VT), Hillary Clinton, Martin O'Malley and Lincoln Chafee take the stage for a Democratic presidential debate sponsored by CNN and Facebook at Wynn Las Vegas on October 13, 2015 in Las Vegas, Nevada. The five candidates are participating in the party's first presidential debate. (Photo by Alex Wong/Getty Images)
- LAS VEGAS, NV - OCTOBER 13: Guests including Senate Minority Leader Harry Reid (D-NV) (4th R) attend a presidential debate sponsored by CNN and Facebook at Wynn Las Vegas on October 13, 2015 in Las Vegas, Nevada. Five Democratic presidential candidates are participating in the party's first presidential debate. (Photo by Joe Raedle/Getty Images)
- LAS VEGAS, NV - OCTOBER 13: Democratic presidential candidate Lincoln Chafee takes part in a presidential debate sponsored by CNN and Facebook at Wynn Las Vegas on October 13, 2015 in Las Vegas, Nevada. Five Democratic presidential candidates are participating in the party's first presidential debate. (Photo by Joe Raedle/Getty Images)
- Presidential hopefuls Bernie Sanders and Hillary Clinton appear on screens in the press room as journalists cover the Democratic presidential debate in Las Vegas, Nevada on October 13, 2015. Democratic presidential frontrunner Hillary Clinton will finally square off with top rival Bernie Sanders in the party's first debate of the 2016 campaign as she seeks to prove she is the candidate to beat. AFP PHOTO/ FREDERIC J. BROWN (Photo credit should read FREDERIC J. BROWN/AFP/Getty Images)