For a president with a loose relationship with the facts and poisonous relationships with allies, the attack on the Saudi oil fields poses a challenge: how to prove the administration’s case that Iran was behind the strike and rally the world to respond.

President Trump must now confront that problem as he struggles with one of the most critical national security decisions of his presidency. Over the next few days or weeks, he will almost certainly face the reality that much of the world — angry at his tweets, tirades, untruths and accusations — could be disinclined to believe the arguments advanced by Secretary of State Mike Pompeo and others that Iran bears responsibility for the attack.

If Mr. Trump tries to gather a coalition to impose diplomatic penalties, tighten sanctions to further choke off Iranian oil exports or retaliate with a military or cyberstrike, he may discover that, like President George W. Bush heading into Iraq 16 years ago, he is largely alone.

Already, intelligence officials are hinting, in background conversations, that the evidence implicating Iran is just too delicate to make public. One theory gaining support among American officials is that the cruise missile and drone attack was launched from southwest Iran or in the waters nearby.