IRAN’S PRESIDENTIAL election has revealed a regime that is concentrating around a core of ruthless ideologues even as its hold on the country is weakening. Ebrahim Raisi, the 60-year-old cleric who was proclaimed the winner of last Friday’s vote, is one of the Islamic republic’s most notorious killers: In 1988, he helped to engineer the execution of thousands of political prisoners. His emergence as a presidential candidate, and as a possible successor to his mentor, Supreme Leader Ali Khamenei, was made possible only by the exclusion of all other prominent candidates, including the reformists who have won several past elections.

The price of that power play was a historic showing of popular disenchantment with the political system. Despite a big campaign to turn out the vote, including a personal appeal from the supreme leader, most Iranians heeded calls from the opposition to stay home. The reported turnout rate of 48 percent was the lowest since the 1979 revolution, and 13 percent of those who did vote cast blank ballots. Though there were no reports of protests, the result bodes poorly for a regime that just two years ago faced street protests across the country — and quashed them by gunning people down with automatic weapons.

Given the outcome, it might seem counterintuitive that diplomats are expressing guarded optimism that the international accord limiting Iran’s nuclear program, ruptured by President Donald Trump in 2018, might be restored in the coming weeks. But even Iran’s hard-liners recognize the need to obtain relief from U.S. economic sanctions. A revived pact could be completed by the outgoing, relatively moderate government of Hassan Rouhani, allowing Mr. Raisi to reap the political benefits after he takes office in August.

The Biden administration, which has made reviving the nuclear deal a priority, can sustain none of the hope its original architect, President Barack Obama, harbored for a moderation of Iranian behavior. A Raisi government will almost certainly continue Iran’s support for Shiite militias in Iraq and Lebanon and for the Palestinian Hamas movement. Mr. Raisi on Monday called Tehran’s regional presence and arsenal of ballistic missiles “not negotiable”; that will make a new deal more difficult, as U.S. officials have said it should depend on Iranian agreement to follow-on talks on those issues. Iranian negotiators are also demanding that the U.S. sanctions on Mr. Raisi, imposed by the Trump administration, be lifted; complying would be an embarrassment for a Biden White House that portrays human rights as central to its foreign policy.

President Biden nevertheless has a good case for going forward. Mr. Trump’s “maximum pressure” campaign against Iran failed to force the regime to accept tighter curbs on its nuclear activity. On the contrary, Tehran increased its stockpile of enriched uranium by a factor of 15, and reduced the time it would need to produce a nuclear weapon to well below the one-year standard set in the accord. While the curbs in a restored deal will expire by the end of this decade, the failure to put them back in place could leave military action as the only means of stopping Iran from producing bombs.

Some in the Trump administration hoped the pressure on the regime would cause its collapse. Instead, it helped to produce the election of Mr. Raisi. Though the United States should continue to oppose Iran’s domestic repression and foreign aggressions with sanctions and support for regional allies, change in the regime must come from Iranians.

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