Vladimir Putin, 72, has not been definitively seen since an appearance at the Valdai Forum in Sochi on November 7 when he congratulated Donald Trump on his election victory

Russian President Vladimir Putin signed a revised nuclear doctrine on Tuesday to effectively lower his country's threshold for using nuclear weapons. Why it matters: The new doctrine suggests Russia could use nuclear weapons to respond to attacks by Ukraine carried out with American support.

After the US allowed Ukraine to use longer-range US-made missiles on Russian targets, Russia’s president updates nuclear-use policy to include more scenarios.