President Trump's tone has shifted both toward Putin and regarding the continuation of U.S. military support for Ukraine.

Russia's nuclear rules say it can use atomic weapons if the country — or one of its allies — is attacked, especially if the attacker is a non-nuclear nation backed by a nuclear power. That clause could be seen as applying to Ukraine,

After Trump sends advanced weapons to Ukraine, Russia warns its nuclear policy is active, raising global tension over NATO's support.