The United States and Iran are locked in a tense and dangerous standoff following President Trump’s decision to kill Maj. Gen. Qasem Soleimani. But while the Iranian regime plots its revenge, its parallel effort to expand its nuclear program could be the spark that ignites a broader conflict.

Iranian officials are now openly threatening to target U.S. assets in the Middle East in response to the Soleimani killing. On Saturday, Trump threatened to attack 52 Iranian sites “if Iran strikes any Americans, or American assets.” (On Tuesday, he backed off his threat to attack cultural sites.) The U.S. military is moving massive resources into the region, and U.S. forces are on high alert in anticipation of a possible military attack.

“I think we should expect they will retaliate,” Defense Secretary Mark T. Esper told reporters Tuesday, saying the retaliation could come from Iranian-backed forces in the region or Iranian forces directly.

But officials and lawmakers say that while Iran contemplates military retaliation, a separate, even more dangerous retaliation is already underway. Iran is promising to relaunch its drive toward having the capability to build a nuclear weapon.

“The play that I think they are going to make in the short term is a dramatic escalation in their enrichment program,” Sen. Lindsey O. Graham (R-S.C.) told me. “A breakout and a race for a bomb is the most likely thing they will do.”

They’ve already started. On Sunday, Iran announced it would no longer abide by restrictions on uranium enrichment under the nuclear deal it struck with the United States and five other powers in 2015. The Iranian government did not specify to what level it would enrich uranium or on what timeline.

Trump responded on Monday by tweeting, “IRAN WILL NEVER HAVE A NUCLEAR WEAPON!” Graham said Trump is signaling that his threat of massive strikes on Iranian infrastructure extends to preventing Iran from achieving a nuclear weapons capability.

“I think when the president says ‘no nuclear weapon for Iran,’ he means it,” said Graham.

Also, because Iranian nuclear sites like the Fordow enrichment facility are buried underground and therefore hard to hit, Trump would most likely target nonnuclear infrastructure like oil refineries, according to Graham.

“If they try to rapidly expand their nuclear program, they might lose their oil program,” he said. “The best way to stop their nuclear program is to crush the Iranian economy.”

Iran’s promise to ramp up its enrichment is surely meant to give Tehran leverage and also to pressure European countries who want to preserve the nuclear deal into pressuring Washington. The Trump administration, having withdrawn from the nuclear deal, is hard-pressed to call for its enforcement now.

By July, Iran had already breached a 300 kilogram limit for its stockpile of uranium enriched to 3.67 percent, a ceiling Tehran had promised to stay under until 2030, according to the nuclear deal. If that stockpile were enriched to higher levels, the timeline for Iran to produce a nuclear bomb would shorten dramatically.

Former national security adviser John Bolton tweeted that Iran’s announcement of enrichment was “another good day” because it revealed Iran had never made the strategic decision to give up nuclear weapons. “Now, it’s on to the real job: effectively preventing the ayatollahs from getting such a capability,” he said.

But the “real job” is actually avoiding a devastating war that would cost untold American blood and treasure and doom the region for a generation. Halting Iran’s nuclear ambitions, while important, is just one piece of that larger puzzle. Diplomacy, sorely needed now, is the only alternative to this conflict.

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