Everything you need to know about the first Democratic debate — VIDEO

Five Democratic presidential candidates are about to try their luck at the first Democratic debate of the 2016 election in Las Vegas on Tuesday night.

Here are 10 of the biggest topics surrounding the first Democratic debate:

Voters aren't aware of the debate

Despite CNN's countdown clock and special live coverage, more than half of U.S. registered voters are not aware of the first debate between the candidates vying for the Democratic presidential nomination, which the news network will broadcast on Tuesday evening.

A Reuters/Ipsos poll of 1,221 adults conducted from Oct. 9 through Oct. 13 found that 57 percent of registered voters were not aware of the debate between the five candidates, to be held at the Wynn Hotel in Las Vegas.

The lack of awareness had little to do with party affiliation. Only 45 percent of voters registered as Democrats knew of the debate, featuring the candidates for their party's nomination in the 2016 election.

In the same vein, 16 percent of registered Democrats said they had heard nothing at all about the debate and 34 percent said they had only heard a little bit.

Only 37 percent of registered voters expect the Democratic event to be as entertaining as earlier Republican debates and 33 percent expect it to be less. Only 29 percent expect it to be more entertaining.

Prepping positions for first debate

In the weeks leading up to the debate in Las Vegas, the two Democrats have been carefully finessing their political positions in relation to each other and their party's wide coalition, offering clues about how they will spar Tuesday night.

Sanders has been signaling he will try to strike a contrast with Clinton on reining in Wall Street and on her record of support for military interventions overseas. The former secretary of state, meanwhile, is under pressure to prove to progressives who have flocked to Sanders that she genuinely cares about the middle class. She's expected to highlight her differences with her rival on gun control and to demonstrate the broad support she has among minority voters -- a key sector of the Democratic coalition where Sanders is struggling.

As he limbered up for their clash, Sanders threw down the gauntlet on the Iraq War -- a thrust that Clinton has struggled to counter in the past -- hinting that she has hawkish views that are out of step with the majority of Democratic voters.

His campaign issued a statement reminding voters that he, then a member of the House of Representatives, voted against authorizing the Iraq war in late 2002. At the time he argued that the conflict would destabilize the Middle East, kill large numbers of Americans and Iraqi civilians and hamper the war on terror against al Qaeda.

The statement did not once mention Clinton -- but it did not have to. The then-New York senator did vote to authorize the Iraq war, and that vote was one of her greatest vulnerabilities in the 2008 Democratic campaign against Obama, who also opposed the war.

Democrats are still urging Biden to run

Draft Biden, the political action committee created to urge Joe Biden to jump into the 2016 presidential race, released on Tuesday a new ad portraying the vice president as an advocate for the dignity of work as he weighs a bid for the White House.

The ad comes after the group pulled a previous ad, which focused on the deaths of Biden's first wife and daughter as a turning point in his life, after Biden reportedly objected.

The group, which is not coordinating its efforts with the vide president, will spend $250,000 airing the new ad on Tuesday ahead of the first Democratic debate and on Wednesday.

"Joe Biden knows that Americans never quit on their country and they always deserve a president who doesn't quit on them," said Brad Bauman, an adviser to Draft Biden, in a statement.

Biden is not expected to appear on the stage, even as speculation swirls that he could announce a run soon.

Which Clinton shows up?

Clinton has spent months on the defensive, due to the controversy over her private email server and surprised by the strong progressive surge that's powering Sanders to her left.

She's come across as not forthcoming in some interviews, reminding voters of the political obfuscation that at times clouded her husband Bill Clinton's administration in the 1990s. Clinton's poll numbers and approval ratings have dipped as a result.

But she's a known strong debater, and went toe to toe with Barack Obama again and again in 2008. A repeat of those assured, likable performances on Tuesday night could go a long way toward reminding 18 million Democrats why they voted for her in her first presidential primary campaign.

Can Clinton flip-flop gracefully?

Hillary Clinton will have to answer for the original sin of politics: flip-flopping.

Clinton came out against the Trans Pacific Partnership last week, when as secretary of state she heralded the agreement as the "gold standard" of trade deals. Her critics quickly accused her of shifting positions for the sake of political expediency in both appealing to liberals and creating distance between her and Barack Obama.

Clinton has also been accused of doing a course reversal on issues important to the Democratic base, like same-sex marriage and whether she supports allowing undocumented people to obtain driver's licenses. She also only recently opposed the Keystone XL pipeline, after months of dodging the question.

Is this Martin O'Malley's only chance?

O'Malley has spent months berating Democratic leaders for failing to schedule more debates, all as he has struggled to climb above single digits in the polls.

Once seen as a fresh and accomplished new Democratic voice, the former Maryland governor -- partly due to his failure to command much media coverage -- is badly in need of a fresh boost of energy.

He and his other underdog rivals, Jim Webb and Lincoln Chafee, will want to emulate Carly Fiorina. The former Hewlett-Packard CEO used fiery performances in the GOP debates to jump-start a stalled campaign and put herself into the top tier of GOP candidates.

O'Malley, 52, is also by far the youngest person on the stage. Sanders is 74, and was born months before America entered World War II. Most of the rest are baby boomers. Clinton is 67, Jim Webb is 69 and served in the Vietnam War, and Lincoln Chafee is 62.

Feel the Bern

By now, Bernie Sanders is used to being the star at the center of the stage.

He's drawing tens of thousands of supporters to campaign rallies, and he's become a liberal sensation, inspiring the popular slogan "Feel the Bern" among progressive Democrats. He's also giving Clinton a run for her money in early states like Iowa and New Hampshire.

Still, the pressure Tuesday night will be like none the Vermont senator has faced so far in the cycle.

Sanders has decades of experience in public office, but in some ways, he seems like a stylistic misfit for the presidential debate stage based on the campaign he has run thus far. He tends to give long and at times rambling speeches, he has repeatedly said he has no interest in attacking his fellow Democratic rivals, and his aides say he's barely engaged in traditional debate prep in the days leading up to Tuesday.

Attacks on Wall Street

Sanders is not alone in seeing Clinton's foreign policy record as a vulnerability. Another Democratic candidate, former Maryland Gov. Martin O'Malley, also picked up on her Syria position Sunday -- saying on CNN's "State of the Union" that a no-fly zone was not advisable and warning that the former secretary of state was "always quick for the military intervention," apparently referring to her previous support for military action in nations such as Iraq and Libya.

Another area where Sanders seems more in tune with the progressive Democratic base is on Wall Street, especially since he has raised most of his money from small donors -- unlike the former secretary of state, who has been relying on big budget fund-raising events with rich contributors. Even with his small-donor focus, Sanders is nearly neck-and-neck in the fund-raising race with Clinton.

Clinton has made strenuous attempts to connect with what her campaign has called "regular" Americans, stressing the need to raise up the middle class to feel the benefits of the economic recovery. But Sanders has said that she hasn't done enough, an argument he may expand upon on the debate stage.

"People will have to contrast my consistency and my willingness to stand up to Wall Street and corporations with the secretary," Sanders said on NBC's "Meet the Press" on Sunday.

The Vermont senator also will likely draw an implied contrast with Clinton on two other issues -- the Trans-Pacific Partnership trade pact the United States and 11 other nations reached this month and the Keystone XL pipeline designed to carry oil from Canada's tar sands across the United States.

Clinton now says she is a 'no' on both issues, but she took months to get there -- despite fervent opposition to both projects from the left flank of the Democratic Party.

Differences on gun control

Guns are one policy issue where Sanders is not completely in sync with the Democratic base, so Clinton is likely to exploit it on Tuesday night.

She has been promising a forthright effort to enact new gun control laws after a string of recent mass shootings. It partly seems to be an attempt to focus attention her rival's record on guns, which recently saw him express his openness to reforms that would hold gun manufacturers liable for crimes committed with their weapons.

Clinton has also spent the runup to the debate cementing her links to key voting blocs of the Democratic coalition -- especially in sectors of the party where Sanders is weak. She can point to broad appeal in the party, which could be key to eventually blunting the challenge from Sanders after early-voting contests in the less diverse states of Iowa and New Hampshire where he is strong.

In recent weeks, Clinton has met representatives of the Black Lives Matter movement and has even criticized Obama for not going far enough in changing immigration laws.

The challenge that Sanders faces reaching out to minority voters, who are a vital part of the Democratic Party voting bloc, was underscored by a new CNN poll Monday finding that only 1% of nonwhite voters in the important early voting state of South Carolina favor him.