Russia is not Iran. Former Russian President Dmitry Medvedev directed this reminder to President Donald Trump on Monday in a social media post. Medvedev, who now serves as deputy chairman of the Russian Security Council, issued what appears to be a not-so-veiled threat in response to Trump’s recent announcement that he has changed his mind about how long he’ll give Russia to strike a peace deal with Ukraine before leveling secondary sanctions against the Kremlin. On Monday, Trump reduced the previous 50-day deadline to “10 or 12” days, prompting Medvedev’s response. “Each new ultimatum is a threat and a step...