Biden warns Putin of sanctions, aid for Ukraine military if Russia invades ReutersBiden voices 'deep concerns' with Putin on Russian aggression against Ukraine Fox NewsBiden told Putin that 'things we did not do in 2014, we are prepared to do now' if Russia escalates in Ukraine, top adviser says CNNBiden, Putin summit: 4 things to know Fox NewsWhy Biden’s threat to sanction Russia probably won’t deter Putin in Ukraine The Independent