5 Things to Watch for at Tonight's Democratic Presidential Debate

With just 15 days until Iowa, here's what to look out for tonight.

CHARLESTON, South Carolina -- Get ready for a showdown.

2) A TANGLE ABOUT WALL STREET: The Sanders campaign released a new ad this week in which the senator says: "There are two Democratic visions for regulating Wall Street. One says it's OK to take millions from big banks and then tell them what to do. My plan: break up the big banks." The Clinton campaign immediately accused Sanders of reneging on a promise not to run negative ads. The senator has stood by his ad and continues to argue that his decision not to take money from Wall Street, as well as his plan for breaking up the country's largest banks makes him tougher on this issue than her. Will she concede on that? Not likely.

4) O’MALLEY'S VALIANT, LAST DITCH EFFORT: There were serious questions as to whether the former Maryland governor would even make this debate after NBC announced polling benchmarks for entry, but O'Malley inched in, just barely. Now tonight, he's likely to give it all he's got in an effort to finally break through in what has become a two-person race.