Two off-duty police officers, who are husband and wife, are credited with stopping a masked robber at a fast-food restaurant in Louisville, Kentucky – and it was caught on video. Naomi Ruchim has the story. Source

The billionaire media mogul’s vast wealth has fueled his run for president, but it could also become a liability. Source

Several people are dead after a mass shooting in a city near Frankfurt. There are reports that victims were shot at two separate hookah lounges. Source

Six candidates will meet on stage at the Democratic debate in Las Vegas on Wednesday night. Source

Two 13-year-old suspects are in custody after a fire in a California library turned deadly. One firefighter who was killed has been identified, and another is missing. Jonathan Vigliotti reports. Source

A Mexican professor living in Singapore is accused of tracking a U.S. government source for the Russian government. He was arrested in the U.S. Jeff Pegues reports. Source

Ahead of Wednesday’s Democratic debate, Democratic National Committee chair Tom Perez spoke with CBS News’ Nikole Killion about the party’s plans to avoid Nevada turning into another chaotic caucus. Source

Former Vice President Joe Biden has touted his support in South Carolina. But after the results from Iowa and New Hampshire, can he maintain his stature there? Emily Bohatch, a politics and government reporter for “The State” newspaper, joined CBSN from South Carolina with more. Source

Erick Diaz Cruz was unarmed when an ICE agent shot him in the face while trying to arrest someone else in Brooklyn. Source

Here’s a look at the top stories making headlines on the “CBS Evening News with Norah O’Donnell.” Source