Incoming President Joe Biden has pledged to work toward returning the U.S. to an era of diplomacy with Iran, after four years of his predecessor’s campaign of “maximum pressure” on that country. But tensions between the two nations have soared anew during Donald Trump’s last weeks as president, with his critics expressing concern that he would order a military strike against Iran. Even without the fresh strains, calming U.S.-Iran relations is a tall order.

1. How serious are worries about Trump ordering a strike?

Serious enough that U.S. House Speaker Nancy Pelosi told fellow members of the Democratic Party Jan. 8 that she’d received assurances from General Mark Milley, chairman of the Joint Chiefs of Staff, that safeguards are in place in case Trump seeks to initiate a nuclear strike, something he has the sole authority to do, or other military action. In the last year, House Democrats have sought to limit Trump’s ability to launch an attack against Iran.

2. What’s produced the latest strife?

The U.S. has piled a wave of new sanctions on Iran and said it was keeping the USS Nimitz in the Persian Gulf because of “recent threats” from its leaders against Trump. Iran’s top nuclear scientist was killed in an assassination widely attributed to U.S. ally Israel. Iran has gone further than before in breaching limits it had agreed to observe under a 2015 deal with world powers to restrict its nuclear program, processing uranium to 20% purity. It seized a South Korean-flagged oil tanker in the Strait of Hormuz. And in episodes that mirror earlier actions blamed on Iran, a ship at the Saudi Red Sea port of Jeddah was hit by an explosion, and a mine was discovered attached to the hull of an oil tanker off Iraq.

3. What’s the ‘maximum pressure’ policy?

In May 2018, Trump withdrew the U.S. from the international agreement under which Iran agreed to limit its nuclear work in exchange for relief from economic sanctions imposed by countries worried it was trying to develop a nuclear bomb. Trump argued he could get a better deal from Iran and began reimposing old sanctions and adding new ones. In May 2019, the U.S. stepped up the pressure by letting waivers expire that had permitted eight governments to buy Iranian oil. As with other sanctions campaigns, U.S. leverage rests with the central role American banks -- and the U.S. dollar -- play in the global economy.

4. Did it work?

Not so far. Rather than leading to a renegotiation of the 2015 accord, the pressure provoked Iran to start violating the deal and, according to its critics, to strike out at the U.S. and its allies largely through proxies and covert actions. U.S. and Saudi officials say that Iran was behind attacks in September 2019 on two Saudi oil production plants that created the single biggest disruption in supply on record. And the U.S. blames Iran for a spate of vessel attacks in the Persian Gulf. Iran denies the accusations.

5. What does Biden say he’ll do?

He’s said he would return the U.S. to the nuclear accord if Iran resumes complying with it. Jake Sullivan, his nominee for national security adviser, has said once that’s accomplished, new negotiations could begin on other issues, including what the U.S. sees as Iran’s malign behavior in the Middle East and the Iranian missile program, which poses a credible threat to U.S. and allied forces in the region.

6. What does Iran say?

Iran takes a similar -- and mutually exclusive position -- that it will come back into compliance with the accord, but only once the U.S. does so by lifting sanctions. Working out the sequencing alone would require considerable diplomacy. Beyond that, Biden will be under pressure from critics of the nuclear deal, both in the U.S. and among its allies, to ease sanctions only if Iran agrees to expand the scope of the original deal. The Iranians are adamantly opposed to that. They’ve said they won’t be drawn into missile talks because the arms are one of the few effective deterrents they have in a region with many U.S. bases and states equipped with military technology far more advanced than theirs. Also, the clock is ticking because the field for Iran’s June presidential election is set to be dominated by conservatives whose influence has surged since the U.S. abandoned the nuclear deal. A hard-line successor to President Hassan Rouhani may not be willing even to reactivate the pact as is.

7. What’s the history between the U.S. and Iran?

Discord between the two countries is rooted in U.S. backing for the 1953 coup ousting Iran’s nationalist prime minister and re-installing the monarch, Shah Mohammad Reza Pahlavi, who was sympathetic to the West. When Islamic revolutionaries took over Iran in 1979, forcing the shah to flee to the U.S., militants seized the U.S. embassy in Tehran and held 52 Americans hostage for more than a year, demanding the shah’s return. The U.S. severed relations and began to impose sanctions, which grew over the years. The U.S. has listed Iran as a state sponsor of terrorism since 1984.

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