Russian President Vladimir Putin may retaliate after President Trump canceled a weekend meeting in Argentina over Russia’s detention of Ukrainian sailors, experts said after the surprise announcement Thursday. About an hour after saying he "probably" would meet Putin at the G-20 summit in Buenos Aires, Trump tweeted that he would cancel the meeting “[b]ased on the fact that the ships and sailors have not been returned to Ukraine,” surprising critics who accused him of being soft on Putin. But the snub — the second this month, after a Paris meeting also was scrapped — may provoke Putin in the near-term,...