The “nuclear option” is a maneuver that allows the majority party to override the Senate’s standing rules with a simple majority vote, as opposed to the usually required two-thirds supermajority. It has most commonly been discussed as a procedural tactic to defuse the threat of a filibuster slowing down or blocking the majority party’s agenda.

Europe's largest nuclear power plant, located in Ukraine but run by Russia, has been cut off from external power for days.

To date, US nuclear doctrine has worked; no one has launched a nuclear attack on the United States, or anyone else, since the end of World War II.

Russia is offering the United States a deal that would extend by one year the last remaining nuclear arms treaty between the two countries, known as New START.

Mr. Putin said Russia didn’t want to provoke a strategic arms race with the United States, but his offer is limited in scope.

A top South Korean official says that North Korea is operating a total of four uranium enrichment facilities, adding to outside assessments that it has multiple covert atomic plants along with the widely known site near the capital of Pyongyang.