For Trump, Threats Become Part of Diplomatic Playbook

President Trump’s threat to impose tariffs on Mexico was met with alarm from business leaders and many in his own party, who responded with corresponding relief when the threat was withdrawn Friday. No one, however, should have been surprised.
Using threats of punitive action even against allies to force negotiation has become a staple of Mr. Trump’s diplomatic playbook, from dangling the prospect of U.S. withdrawal from the North Atlantic Treaty Organization if Western nations didn’t increase their contributions to, in this case, hitting one of the U.S.’s largest...