"The Circus" co-host Alex Wagner on what she learned from Elizabeth Warren's massive NYC rally

Season Four of Showtime's political docuseries "The Circus" returns Sunday ahead of the 2020 primary season. National polls show the race for the Democratic nomination narrowing between former Vice President Joe Biden, Senator Elizabeth Warren and Senator Bernie Sanders. Wagner joins "CBS This Morning" to discuss the massive New York City rally Elizabeth Warren held earlier this week and what that means for the Democratic nomination.