Russia has followed up its recent incursions against Poland with threats to other NATO members. Nineteen Russian drones, many originating from Belarus, crossed into Polish airspace late Tuesday, forcing the Eastern European nation to shut down four of its airports as it scrambled to fire up its defense systems. Polish Prime Minister Donald Tusk invoked Article 4 of the NATO Treaty the following day, calling the ​​situation the “closest” that Poland had come to armed conflict since World War II.