President Donald Trump issued a rare threat of nuclear escalation on Friday, saying he had ordered two nuclear submarines to be strategically positioned near Russia in response to what he said were aggressive remarks by Dmitry Medvedev, the country’s former president and current deputy chairman of its Security Council. “I have ordered two Nuclear Submarines to be positioned in the appropriate regions, just in case these foolish and inflammatory statements are more than just that. Words are very important, and can often lead to unintended consequences, I hope this will not be one of those instances. Thank you for your...