President Joe Biden said Thursday that the risk of nuclear “Armageddon” is at the highest level since the 1962 Cuban Missile Crisis, as Russian officials speak of the possibility of using tactical nuclear weapons after suffering massive setbacks in the eight-month invasion of Ukraine.

Speaking at a fundraiser for the Democratic Senatorial Campaign Committee, Biden said Russian President Vladimir Putin was “a guy I know fairly well” and the Russian leader was “not joking when he talks about the use of tactical nuclear weapons or biological or chemical weapons.”

Biden added, “We have not faced the prospect of Armageddon since Kennedy and the Cuban Missile Crisis." He suggested the threat from Putin is real “because his military is — you might say — significantly underperforming.”

U.S. officials for months have warned of the prospect that Russia could use weapons of mass destruction in Ukraine as it has faced a series of strategic setbacks on the battlefield. As recently as this week, though, they have said they have seen no change to Russia’s nuclear forces that would require a change in the alert posture of U.S. nuclear forces.