When it comes to presidential debates, moderators most certainly matter. When the three contenders for the Democratic nomination for president -- former Secretary of State Hillary Clinton, former Maryland Gov. Martin O'Malley and Sen. Bernie Sanders, I-Vt. -- take the stage again Saturday night for the third Democratic debate, two people are supposed to keep the conversation moving, civilized and, of course, productive. They are Martha Raddatz, ABC News' chief global affairs correspondent and a veteran at the network, and David Muir, anchor of World News Tonight. 

Raddatz, who served as White House correspondent during the last term of President George W. Bush, previously moderated the October 2012 vice presidential debate between Rep. Paul Ryan and Vice President Joe Biden, garnering praise for her sharp questions and control of the debate. She has reported from Pakistan, Afghanistan, Iraq, India and countries in Africa and has been part of a team whose coverage won an Emmy Award, according to her official ABC News biography.

Muir became the anchor of ABC's World News Tonight in September 2014. He has been at ABC since 2003 and covered stories from Hurricane Katrina to the 2008 Beijing Summer Olympics, according to his ABC News biography. He has interviewed several prominent world leaders, including Pope Francis and President Barack Obama, as well as one of the participants in Saturday's debate, Hillary Clinton.

The debate is scheduled to air on ABC at 8 p.m. EST and is being held at St. Anselm College, in Manchester, New Hampshire, co-hosted by ABC News, the New Hampshire Democratic Party and local news outlet the Union Leader. Unlike previous debates, rules and formatting are not expected to be released prior to the contest.

Three Democratic debates have been scheduled for 2016. The next is expected to be held in Charleston, South Carolina Jan. 17 and hosted by NBC News and the Congressional Black Caucus Institute.