US President Joe Biden speaks at a press conference on December 8, 2021. (Photo: AFP/ Getty Images)

Speaking to reporters as he left the White House for a trip to Kansas and Missouri, Biden said the United States has a moral and legal obligation to defend NATO allies if they are attacked, but that obligation does not extend to Ukraine. But it will depend on what the rest of the NATO countries want to do, he added. The US unilaterally using force to confront Russia if it invades Ukraine is not in the cards right now.