Washington — It’s a good rule never to start a fight you’re not eager to finish. But the Trump administration and its Arab allies now seem caught in a version of that dilemma with Iran, which is proving to be a tougher adversary than Washington expected.

Iran’s alleged attack last Saturday on Saudi oil facilities caught U.S. analysts by surprise. It was a major strike, using a combined force of 25 Iranian ballistic missiles and drones, according to Saudi officials, against assets that were supposedly protected by U.S. and Saudi defensive weapons.

For U.S. officials, one message is that the Iranians are much more militant and risk-tolerant than American analysts had believed. Another is that the Iranians have correctly assessed that President Trump doesn’t want war and are taking advantage of that perceived weakness. The more Trump talks about his desire for a diplomatic solution, the more Iran seems ready to attack. That’s a dangerous dynamic.

America has enormous military power in the Gulf, enough to obliterate Iran many times over. But the unpleasant fact is that Iran hasn’t been deterred by this force. That’s a situation strategic planners dread, because it can drive a nation toward conflict simply to demonstrate its credibility and avoid a larger battle.

U.S. officials describe Iran’s denials of responsibility for the Saudi strike as bald lies. They say that intelligence leaves no doubt that the attacks originated inside Iran, though officials are wary of revealing publicly how much they know about Iranian operations. Col. Turki al-Malki, a Saudi military spokesman, said bluntly Wednesday in displaying fragments of Iranian munitions: “The attack was launched from the north and unquestionably sponsored by Iran.”

Iran’s attack on the Saudi refinery at Abqaiq was a potential game changer for oil markets. It showed the vulnerability of energy infrastructure — not just in Saudi Arabia but among its Gulf neighbors: Kuwait, Bahrain, Qatar and the United Arab Emirates. These countries have made huge investments in U.S. military systems that, it turns out, leave them vulnerable.

Energy analysts must assume that such an attack could happen again, against multiple targets, unless the U.S. launches retaliatory strikes that would themselves pose big risks for Gulf energy shipments. Thus, upward pressure on oil prices could continue for months and maybe years — not the message Trump wants as he prepares for an election year.

But for Trump, this is a self-inflicted wound. As the confrontation escalates, it’s important to remember that it was entirely unnecessary.

Trump chose to abandon the 2015 Iran nuclear agreement, against the advice of most of his allies and many of his senior aides, and despite Iran’s compliance with the deal. He apparently wanted a bigger, better deal that would outdo President Obama’s version. And he seemed certain that if he applied “maximum pressure” through economic sanctions, Iran would come to the table.

Instead, starting in May, Iran launched an escalating campaign against Saudi and UAE oil targets. With Trump’s blessing, the U.S. adopted a low-key response. Even after Iran shot down a U.S. surveillance drone in June, Trump personally decided against a military response.

Some national security officials worried that this reticence might weaken deterrence, but Trump wanted to avoid war. He understood that another major conflict in the Middle East would be a political disaster, especially in defense of a Saudi Arabia that’s unpopular with many in Congress.

Trump has continued to seek talks with Iran, despite warnings from some analysts that Iran’s Supreme Leader Ali Khamenei would refuse. Trump encouraged mediation efforts by Japanese Prime Minister Shinzo Abe and French President Emmanuel Macron, but those were spurned by Tehran, as was Trump’s suggestion of a meeting this month in New York with President Hassan Rouhani.

Against a cocky Iran, the Trump administration continues its relatively soft line. Secretary of State Mike Pompeo said this week that last Saturday’s attacks were an “act of war.” But Thursday, he blandly countered Iranian Foreign Minister Mohammad Javad Zarif’s threat of “all-out war” against any retaliation with the assurance that his goal was “achieving peace and peaceful resolution.”

The Iran confrontation converges on three painful realities: Iran is now a full-fledged menace to security and oil shipments in the region; any military action against Iran must include some Saudi forces for it to be politically acceptable in America; Saudis and Emiratis, seeing anew their vulnerability, are wary of open conflict.

This dangerous chain of events was predictable — and indeed, predicted. Now Trump must decide whether to fight a war he and the country don’t want, or to accommodate an Iran whose truculence he helped create. Welcome to the Middle East, Mr. President.

— David Ignatius is a columnist for Washington Post Writers Group.