Open this photo in gallery: Russian President Vladimir Putin, right, and North Korea's leader Kim Jong Un shake hands during their meeting in Vladivostok, Russia on April 25, 2019.Alexander Zemlianichenko/The Associated Press North Korean leader Kim Jong-un may travel to Russia for a summit with President Vladimir Putin, a U.S. official said, in a trip that would underscore deepening cooperation as the two isolated leaders are locked in separate confrontations with the U.S. U.S. officials also said that Russia is seeking to buy ammunition from North Korea to refill reserves drained by its war in Ukraine. In return, experts said,...