Tamara Keith and Amy Walter on Iowa and Sanders vs. Warren

NPR’s Tamara Keith and Amy Walter of the Cook Political Report join Judy Woodruff to discuss the latest political news, including shifting poll numbers from Iowa that show strength for former Vice President Joe Biden, the withdrawal of Sen. Cory Booker from the 2020 presidential race, signs of animosity between Sens. Elizabeth Warren and Bernie Sanders and what President Trump is tweeting.