As the Iowa Caucuses loom, the three candidates for the Democratic nomination for president will meet  Sunday night in a debate in South Carolina.

Former Sen. Hillary Clinton, Sen. Bernie Sanders (D, Vermont), and former Maryland Gov. Martin O’Malley will answer questions in the NBC News-hosted event as the race has tighten in advance of  the caucuses (Feb. 1) and the New Hampshire primary (Feb. 9).

The most recent polls show what  was a strong lead for Clinton in Iowa has eroded as Sanders’ support has stayed strong in New Hampshire.

The latest Bloomberg Politics/Des Moines Register poll showed Clinton leading Sanders by 2 percent in Iowa, with a Marist/Wall Street Journal/NBC News poll showing Sanders up by 14 percentage points in New Hampshire.

Here’s a quick look at how and what to watch for in Sunday’s debate.

When: Sunday, Jan. 17

Where: Charleston, S.C.

What time:  Pre-debate coverage starts at 8 p.m. (ET) on NBC  channels  and  YouTube.  The debate starts at 9  p.m. (ET)

Hosted by: NBC

Airs on: NBC and YouTube. To find your local NBC channel enter your zip code on these sites: (Dish TV); (DirecTV); (AT&T U-verse).Or you can watch it online via the NBC News Android App, the Amazon App or FireTV, the NBC News app or  Roku.

Live stream: The debate will be streamed live here.

Moderators: Lester Holt will be the principal moderator, with NBC News' chief foreign affairs correspondent Andrea Mitchell, as a co-moderator. Chuck Todd of "Meet the Press," will anchor coverage before and after the debate.

Who's in: Here are the candidates participating in tonight's debate and their websites. Candidates had to average at least 5 percent support either nationally or in the first three nominating states of Iowa, New Hampshire and South Carolina "in the five most recent polls recognized by NBC News," NBC reported.

•    Hillary Clinton

•    Bernie Sanders

•    Martin O'Malley

Likely issues

While we don't know for sure, the likely issues to be raised in the debate include:

1. Gun control

2. Health care

3. National security

4.  Taxes

5. Health of the national economy

When's the next one

The next Republican debate will be held, Jan. 28, 2016  at the Iowa Events Center in Des Moines, Iowa. It will be hosted by Fox News. The next Democratic debate will be on Feb. 11,  in Wisconsin. It will be hosted by the  Public Broadcasting System.