In 2012, President Obama made it plain in a letter to Iranian supreme leader Ayatollah Ali Khamenei that any attempt to close the strategic Strait of Hormuz would be met with American force.
Yet when Iranian Revolutionary Guard Corps gunboats seized the Marshall Islands-flagged container ship Maersk Tigris near the strait April 28, sending a shudder through global markets, U.S. officials held their fire.
They condemned the move, dispatched naval escorts for some U.S.- and British-flagged vessels, but didn't challenge the Iranian military during the nine days it held the vessel in what Iran called a legal dispute.
Administration officials said their response was prudent. But critics in the region and the United States saw it as more evidence that the administration is sidestepping conflict with its longtime adversary in Tehran to avoid undermining negotiations that U.S. officials hope will produce a landmark nuclear agreement with Iran at the end of this month.
"They want to appease the Iranian regime," said Ahmad El Assaad, a prominent Lebanese political leader who opposes the U.S. lowering its guard against Iran or its proxies. "They've invested so much in this deal they want to do everything possible to get it done, even if it means turning their back on friends."
The administration denies it is going soft on Iran, or easing support for allies. Even critics acknowledge they can't be sure what motivates specific administration moves.
But the anxiety among U.S. allies in the Middle East is real, and it suggests strains on core U.S. alliances are likely to remain a challenge for the administration if a nuclear deal is completed, as expected.
"The perception problem is real," said Daniel Kurtzer, a former U.S. ambassador to Israel and onetime Obama campaign advisor.
Criticism from Arabs, Israelis and some in the United States has mounted during the 22 months of talks between Iran and a diplomatic bloc consisting of the United States and five other major powers — France, Britain, Germany, Russia and China. They are seeking an agreement that would block Iran's ability to build a nuclear bomb in exchange for easing international economic sanctions.
One stumbling block to an agreement emerged Sunday when the Iranian parliament voted to ban international inspectors from entering military bases as part of the nuclear deal. The measure, if approved by an oversight body, could complicate the bargaining because the six powers say they need to get onto military bases to verify that Iran isn't seeking to build a bomb.
Many in the region fear Obama is seeking not just a legacy-burnishing foreign policy victory, but a new relationship with Tehran that might diminish the support their countries get from Washington.
The critics worry that the administration is scaling back efforts to confront Iran's military and armed proxies, slowing its sanctions effort, and playing down Iran's sponsorship of terrorism. They fear the deal will go too far to strengthen Iran, including the release of $150 billion in now-frozen overseas funds.
Critics saw the administration's caution in its response to the seizure of the Maersk Tigris near the Strait of Hormuz. Nearly a third of the world's seaborne oil shipments use the narrow Persian Gulf outlet.
Iran claimed it ordered the ship into an Iranian port because Maersk, a Danish shipping giant, had failed to deliver about $4 million in goods to an Iranian firm. The move followed days of Iranian harassment of cargo ships in the strait, including an incident in which gunboats trailed a U.S.-flagged vessel, the Maersk Kensington.
The United States is obliged to protect Marshall Islands-flagged ships under a treaty with the tiny Pacific nation. Yet the administration kept its efforts low-key, despite accusations from House Speaker John A. Boehner (R-Ohio) that it was taking the threat too lightly. The ship and its 24 crew members were released without harm May 7.
Every U.S. administration since the 1979 Iranian Revolution has sought to prevent Iran from destabilizing its neighbors and to isolate it diplomatically. In its first five years, the Obama administration sanctioned hundreds of Iranian groups and individuals in hopes of building pressure that would force Iran to negotiate limits on its nuclear program.
Some administration critics contend sanctions enforcement has eased in the last two years. U.S. officials insist they're keeping up the pressure, and have sanctioned 100 Iranian individuals and groups since nuclear negotiations began in November 2013.
Countries also have filed fewer reports since then that Iran is violating sanctions by buying banned arms-related goods, according to a report this month by the United Nations' committee on Iran sanctions. But it's unclear whether Iran has sought to buy less illicit hardware, or if countries have shown "restraint" in reporting violations "so as not to affect the negotiations process," the report says.
U.S. officials long have described Iran as the world's chief state sponsor of terrorism. But when Director of National Intelligence James R. Clapper issued an annual report to Congress on worldwide threats in February, Iran's role in promoting terrorism received no mention at all, drawing protests from some senators.
Arab states have worried for years that the administration's refusal to expand military operations against the Iranian-backed Syrian government reflected its desire to seal the nuclear deal and improve its ties to Tehran. Now they fear they see the same in Washington's tacit cooperation with Iranian-backed Shiite Muslim militias in Iraq against the militant group Islamic State.
U.S. officials insist they continue to aggressively enforce sanctions, and to confront Iran in the region.
The administration is providing logistic and intelligence support to the Saudi-led air campaign against Iranian-backed Houthi rebels in Yemen, for instance, and has deployed warships to prevent Iran from shipping weapons to the Yemeni insurgents.
"There's no pulling our punches, even during these negotiations," Samantha Power, the U.S. ambassador to the U.N., told a House subcommittee last week.
Even so, uneasy allies "see a lack of energy from the U.S. compared to what it used to do to counter Iran's behavior," said Michael Singh, managing director of the Washington Institute for Near East Policy.
Also worrying to the critics are the administration's varying statements about its goals for the deal. Obama and other U.S. officials have long insisted that the nuclear deal is aimed at preventing Iran from getting a bomb, and not designed to open a new relationship with Tehran.
But at other times Obama has said an accord could open the way to a more moderate Iran with stronger ties to the outside world and better relations with the United States.
A successful deal would allow Iran to become "a very successful regional power that was also abiding by international norms and international rules," Obama said in December. "And that would be good for everybody."