President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE’s opportunity at next week’s G-20 summit to reset U.S. relations with close allies is a particularly timely one, for it comes as Washington suffers the downsides of its frayed relations in connection with one of its biggest global challenges of the moment — its rising tensions with Iran.

After launching a pressure campaign against Iran by withdrawing from the 2015 global nuclear deal and re-imposing economic sanctions that are squeezing Iran’s economy and causing serious hardship among its people, Washington is now blaming Tehran for recent attacks on tankers in the Gulf of Oman and sending another 1,000 troops to the region to monitor Iranian activities and protect the troops already there.

And yet, in its efforts to force Tehran to negotiate new limits on its nuclear and ballistic missile programs, and to abandon its wicked ways in the region and beyond, it is Washington that finds itself largely alone.

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Particularly telling are the suspicions in European capitals and elsewhere that Trump’s fingering of Tehran for the tanker attacks looks eerily like the events of 1964 that prompted the Gulf of Tonkin resolution — which gave President Lyndon Johnson broad authority to wage the Vietnam War but which later raised suspicions that he invented or exaggerated the North Vietnamese attack that drove the resolution.

“There’s a lot of suspicion in Europe about American motives,” a French defense analyst told the New York Times in a sentiment echoed by others. “The maritime milieu is especially susceptive to manipulation — remember the Gulf of Tonkin.”

In essence, the chickens of Trump’s unilateralism, his efforts to pressure U.S. allies to back his policies rather than convince them to do so, his threats to impose tariffs on them if he doesn’t get his way, his sometimes sizable swings in policy on such issues as North Korea’s nuclear program, and his propensity to slight the leaders of allied nations on a personal level, are all coming home to roost.

To be sure, the United States and its allies agree that Iran is a dangerous regional player, that it will be much more dangerous if it develops nuclear weaponry, and that the global community should contain it. But on each major aspect of the Iranian challenge, the United States and its allies are moving in different directions.

On the nuclear deal, Tehran shrewdly widened the breach between America and its allies by announcing that, by the end of this month, it will exceed the deal’s limits on Iranian stockpiles of low-enriched uranium — unless the Europeans find a way for Iran to evade U.S. sanctions. The regime also threatened to enrich its uranium to a higher purity, which would make converting the fuel to a nuclear-grade level much easier.

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Washington and Europe’s signatories to the deal (Britain, France, and Germany) have been moving in starkly different directions on the deal for some time. When Trump withdrew, the Europeans sought to work with Iran to salvage the deal. When Trump re-imposed sanctions, European leaders sought (though so far without success) to create a system that would enable its firms to continue doing business with Iran and evade the sanctions by participating in a system of barter trade.

As for the tanker attacks, one need not be a Trump supporter or a hardline Iran critic to believe that Tehran was behind them.

For one thing, such attacks would signal a return to Iran’s maritime mischief of decades earlier, which prompted the U.S. Navy to destroy half of Iran’s fleet in 1988 after an Iranian naval mine nearly sank a U.S. frigate in the Persian Gulf. For another, even House Intelligence Committee Chairman Adam Schiff Adam Bennett SchiffSchiff claims DHS is blocking whistleblower's access to records before testimony GOP lawmakers distance themselves from Trump comments on transfer of power Rubio on peaceful transfer of power: 'We will have a legitimate & fair election' MORE, a fierce Trump critic, acknowledged the overwhelming evidence that Iran is to blame.

Nevertheless, Trump’s credibility issues, and America’s lingering credibility issues related to Iraq and the ill-fated search for weapons of mass destruction, have left our closest allies wary of believing U.S. contentions.

Such wariness could complicate any U.S. effort to protect ships passing through the Strait of Hormuz. Since the United States reportedly lacks the requisite number of ships to do the job itself, it would need to build a coalition of nations that our disgusted and distrustful allies may be reluctant to join.

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We are a long way from the days of the Cuban Missile Crisis, when French President Charles de Gaulle told former Secretary of State Dean Acheson that he didn’t need to see the proof of Soviet missile activity in Cuba because “The word of the President of the United States is good enough for me.”

At next week’s G-20 gathering in Osaka, Trump would be wise to begin repairing the damage of more recent times.

Lawrence J. Haas, senior fellow at the American Foreign Policy Council, is the author of, most recently, "Harry and Arthur: Truman, Vandenberg, and the Partnership That Created the Free World."