The Trump administration and its domestic political allies are laying the groundwork for a possible confrontation with Iran without the explicit consent of Congress — a public relations campaign that was already well under way before top officials accused the Islamic Republic of attacking a pair of oil tankers last week in the Gulf of Oman.

Over the past few months, senior Trump aides have made the case in public and private that the administration already has the legal authority to take military action against Iran, citing a law nearly two decades old that was originally intended to authorize the war in Afghanistan.

In the latest sign of escalating tensions, National Security Adviser John Bolton warned Iran in an interview conducted…