Just weeks ahead of voters heading to the polls in Iowa and New Hampshire, the Democratic presidential candidates meet Sunday for their fourth debate, but the first in 2016. With the top of the polls tightening, all eyes will be on front-runner and former Secretary of State Hillary Clinton and Vermont Sen. Bernie Sanders.

Also joining the field will be former Maryland Gov. Martin O'Malley, who is averaging just 4.6 percent support in Iowa. NBC News, which is hosting the debate, had previously said a candidate needed to register at least 5 percent support in Iowa, New Hampshire or South Carolina to qualify for the event. But an NBC executive familiar with the situation told CNN the network would round up from 4.5 percent if necessary — meaning viewers would get to watch the three-person field that has become familiar. 

Heading into the weekend, O'Malley trailed Clinton and Sanders by a significant margin. The RealClearPolitics average of polls indicated Clinton registered 48.3 percent support nationally, Sanders 39.7 percent and O'Malley 2.3 percent. 

With the top of the polls tightening, Clinton and Sanders will look to have a strong showing at the debate in Charleston, South Carolina, ahead of the Feb. 1 Iowa caucuses. The Washington Post reported Thursday Clinton's lead is slipping much faster in 2016 than it did in 2008 when she lost the nomination to President Barack Obama. Clinton leads Sanders by just 2 percentage points in Iowa, a figure that falls well within the margin of error, a recent Des Moines Register/Bloomberg Politics poll indicated. Last month, Clinton led by 9 percentage points. 

Read below for all the information needed to watch the debate:

Start time:  9 p.m. EST

TV channel:  NBC

Online: NBC News and YouTube are co-hosting the event and streams will be available on both. 

Apps: For all the cord-cutters, here are a few other options. NBC said the debate will be available on the NBC News app and Amazon Fire TV. It will also be available on Apple TV through the tvOS Appstore and on Roku.

Radio: Click here to find your local station to listen live.