Anderson Cooper 360

The Known Unknown; U.S. Sends Draft Letter To Iraqi Govt. Suggesting U.S. Would Withdraw Troops, Then Says It Was A "Mistake"; U.S.: Letter To Iraq Suggesting Troop Withdrawal A "Mistake"; Defense Secretary Contradicts Pres. Trump On Targeting Cultural Sites; Esper: "We Will Follow The Laws of Armed Conflict"; Sanders On U.S. Mistaken Letter To Iraq On Troop Withdrawal: "It's Mass Chaos"; Sen. Sanders Talks The State Of The 2020 Race; John Bolton: If The Senate Subpoenas Me, " I Am Prepared To Testify"; Sanders Tied With Biden And Buttigieg In Iowa, Leads Field In New Hampshire In New CBS/YOUGOV Polls; Defense Secretary Contradicts Pres. Trump On Targeting Cultural Sites; Esper: "We Will Follow The Laws Of Armed Conflict"; Sanders: Biden "Brings Into This Campaign A Record Which Is So Weak"; One-On-One With Se. Bernie Sanders; Bolton: "I Am Prepared To Testify" In Impeachment Trial If Subpoenaed; Bolton Says After "Care