Mr. Trump’s ability to respond effectively is severely limited compared to previous U.S. presidents. Few believe his pronouncements, so barring the presentation of overwhelming evidence, claims of Iranian responsibility will not persuade even close U.S. allies. European states that joined U.S. operations to secure the Persian Gulf in the past are very reluctant to do so now, because they fear Mr. Trump will drag them into a war. Even some of Iran’s foremost adversaries don’t want a conflict with Iran presided over by an erratic and unstable U.S. president, who already canceled one military strike at the last minute.

The attack should not go unanswered, but the best response may not be a military one. Mr. Trump risks compounding his strategic problems if he acts hastily or recklessly. The United States must first work to definitively establish who was responsible for the operation and how it was carried out, and make that information public. Especially since it was Saudi and not U.S. assets that were struck, no retaliatory U.S. military action should be undertaken without consultation with Congress.