Ukraine is on high alert after the U.S. warned an attack could be “imminent.” Several Ukraine airports closed as Ukrainian President Zelensky said the “trigger” for Russian invasion could happen at “any minute.” William Cohen served as the Secretary of Defense during the Clinton administration. He tells Anderson Cooper how far he thinks the Biden administration should go with sanctions against Russia. Plus, President Zelensky said he tried to call Russian President Putin but was unsuccessful. Steve Hall is the former CIA Chief of Russia. He joins AC360 to discuss what Putin’s rationale could be for invading Ukraine.