The Democratic Party's presidential hopefuls will take the debate stage for a second time Saturday night, and this time no one will keep a spot reserved for U.S. Vice President Joe Biden. Candidates, including former U.S. Secretary of State Hillary Clinton and Vermont Sen. Bernie Sanders, will square off at the CBS/Twitter-hosted event at Drake University in Des Moines, Iowa, at 9 p.m. EST.

Biden announced Oct .21 that he won't run for the White House in 2016, while former Rhode Island Gov. Lincoln Chafee and former Virginia Sen. Jim Webb dropped their presidential campaigns after the first debate, held Oct. 13. This means Clinton, the Democratic front-runner, Sanders and former Maryland Gov. Martin O'Malley will participate in Saturday's debate.

Clinton is enjoying a strong lead nationally in the polls. One poll recently conducted by CBS News and the New York Times showed 52 percent of Democratic primary voters support Clinton, while 33 percent backed Sanders and 5 percent support O'Malley. Clinton has a large advantage among women voters and a narrow lead with men, while Sanders has the edge with Democrats under age 45. But half of Democratic voters say they haven't yet picked a candidate, according to the poll -- which was conducted by telephone Nov. 6-10 among a random sample of 1,495 adults nationwide, including 1,259 registered voters.

With less than three months to go until the start of the nominating contests, Saturday's debate could shake things up for the White House hopefuls. Here are the rules for Saturday's debate:

Supplies: The three participating candidates can't bring much of anything with them to the debate. That means no cell phones, tablets, notes or props to help illustrate points. But each candidate will be given a notepad, pen and glass of water.

Opening statements: Unlike previous debates, CBS News said there will be no opening statements, according to Politico.

Questions: John Dickerson, host of CBS's "Face the Nation," will moderate the two-hour debate. CBS is partnering with Twitter, which will provide reaction and viewer questions during the Democratic showdown. You can participate by using the hashtag #DemDebate and tag one of the candidates' Twitter handles

Subjects: Rising income inequality and stagnating wages were expected to be hot debate topics. The candidates will also be able to express their views on healthcare, education, retirement and other economic issues.

Answer time: Each candidate will have 60 seconds for their initial answer to a question, plus 30 seconds for rebuttals.

Closing statements: Participating candidates will have 60 seconds for closing statements at the end of the showdown, which will be broadcast by CBS News in conjunction with network affiliate KCCI-TV and the Des Moines Register.