5 Storylines to Watch at Tonight's Presidential Debate

ST. LOUIS, Missouri— -- The second presidential debate caps off a news-filled week on the campaign trail and expectations are high that tonight will be quite a showdown.

Hillary Clinton and Donald Trump are expected to face off in front of a large television audience, a viewing audience and a select group of undecided voters, some of whom are slated to ask the candidates questions directly in the town hall-style format of tonight’s debate.

Watch the second presidential debate, co-moderated by ABC News’ Martha Raddatz, on ABC News and ABCNews.com at 9 p.m. ET on Sunday, Oct. 9.

Here are five of the most important storylines to watch when tuning in at 9 p.m.

How Trump Explains Himself

The release of a recording of a vulgar conversation Trump had in 2005 brought chaos to the campaign on Friday night and into this weekend.

On the recording, Trump is heard describing his failed efforts to hit on a married woman and his habits of "grabbing [women] by the p****," which he says he is able to do because of his fame.

The release of the recording prompted widespread condemnation by Republican party leaders and several withdrawals of support by other politicians who had initially endorsed their party's nominee.

Trump has already responded to the recording several times -- immediately putting out a statement calling it "locker room banter," later releasing a video apology -- but the audience at the debate will inevitably be the largest one he faces following the scandal.

Practice Potentially Paying Off

Much attention was paid to the preparation that Clinton and Trump did and didn't do, respectively, before their first debate last week.

After Trump's performance was widely criticized, he reportedly spent some more time preparing for this debate, though the different format of tonight’s event meant that he had to do so in a different way.

The clearest example of his efforts to prepare for tonight's debate came earlier this week in New Hampshire where a group of invited supporters were able to ask him questions, and his answers were timed to match the amount of time he will be given under the Commission on Presidential Debate's rules for tonight's town hall.

In spite of the similarities, Trump denied that the event was held as a type of mock debate.

Completing the Tickets

While Clinton and Trump have long been the stars of the show during this general election season, their running mates were the ones to take center stage earlier this week.

Sen. Tim Kaine regularly interrupted Gov. Mike Pence. Pence won praise for looking comparatively calm, though he did repeatedly deny correct claims by Kaine about some of Trump's policy positions, raising questions about how familiar he actually is with his running mate and their proposals.

Tonight will be an opportunity for Clinton and Trump to take back the spotlight and make another case for why they believe they should be elected.

Connecting With Voters

The town hall-style format is decidedly different from the other two presidential debates because they have to face voters directly.

In the past, the town hall debates have been make-or-break for certain candidates, as they're able to show their compassionate side as they are given the chance to connect with voters.

That worked with Bill Clinton in 1992, and didn't for then-President George H.W. Bush, who was spotted checking his watch during their televised town hall. More recently, the town hall debate helped boost President Obama's support following a lackluster performance at his first debate against Mitt Romney in 2012.

The Role of the Moderators

One difference between this year's town hall and the ones in previous elections comes in the form of the moderators. In 2012, CNN's Candy Crowley was the moderator of the town hall debate, but this year the CPD decided to have two moderators -- ABC News' Martha Raddatz and CNN anchor Anderson Cooper.

There has been a lot of pressure put on the moderators during this election, since the two campaigns have different views on whether the moderators should be able to fact-check the candidates in real time.

Fact checking was specifically an issue in the Crowley town hall, when she corrected a claim made by Romney, which was controversial at the time.

Watch FULL LIVE COVERAGE of the second presidential debate, co-moderated by ABC News’ Martha Raddatz, at 9 p.m. ET on Sunday, Oct. 9. Coverage and analysis of the debate will begin on ABCNews.com/Live at 7 p.m. ET.