And this week, three officials said, the Navy is likely to begin moving an aircraft carrier task force toward the Persian Gulf, as a hedge against unanticipated events.

The show of force comes as the Trump administration is drawing down U.S. troops in three Centcom battle zones: Afghanistan, Iraq and Somalia. The Pentagon’s message to Iran seems to be a cautionary warning against exploiting the situation, rather than a direct threat. But the confrontation over Iran’s nuclear program looms in the background.

Iran, too, has been signaling its firmness — along with its willingness to revive diplomacy with the new administration of President-elect Joe Biden. Tehran’s potential threat was underscored this month by the United Nations’ International Atomic Energy Agency, which reported that Iran’s stockpile of low-enriched uranium is now 12 times the level permitted under the 2015 nuclear agreement, which Trump abandoned in 2018. The IAEA said Iran is also adding more advanced centrifuges to speed enrichment.

Iran has been hoping to wait out Trump’s presidency, and that theme was reinforced last week by Foreign Minister Mohammad Javad Zarif. He said Iran would revert to the 2015 limits if the new administration returned to the deal, too. “This needs no negotiations and needs no conditions,” he said.

Anti-Iran hawks in the United States and Israel see the window closing on the possibility of a preemptive U.S.-Israeli strike against the Iranian nuclear program. Likely supporters of such an attack include Israeli Prime Minister Benjamin Netanyahu and some hard-line officials around Trump. Netanyahu has said often that the potential Iranian nuclear threat represents an existential issue for Israel, and the chance to land a knockout punch may expire Jan. 20.

“There must be no return to the previous nuclear agreement. We must stick to an uncompromising policy to ensure that Iran does not develop nuclear weapons,” Netanyahu told an Israeli audience this week.

Trump considered a strike on Iran earlier this month but decided against it. Worried by the IAEA reports that Iran was increasing its uranium stockpile, Trump on Nov. 12 requested military options. He was dissuaded from taking action by Chairman of the Joint Chiefs of Staff Gen. Mark A. Milley, Secretary of State Mike Pompeo and other officials. Trump decided it would be unwise to start a new war with unpredictable consequences in his last two months in office. But several officials say the possibility isn’t entirely foreclosed, and, as one official put it, “we’re not out of the woods yet.”

Skeptics about attacking Iran include senior military officers in both the United States and Israel, who fear a chain reaction that would leave all sides worse off. One former top defense official warns that the idea of a “clean, limited, surgical strike” against Iranian nuclear facilities is folly; war doesn’t work that way. U.S. intelligence agencies also caution that despite the troubling IAEA reports, Iran remains many months away from being able to deploy a bomb.

Several insiders stress that Trump doesn’t want a new conflict in the Middle East that would undermine what he sees as his legacy of stopping “endless” wars there. But squeezing Iran’s nuclear program has also been one of his signature issues, and he’d probably like to tighten the pressure further before leaving office.

Elliott Abrams, Trump’s special envoy for Iran, stressed nonmilitary options in comments this week: “All through December and January, there will be sanctions that deal with arms, that deal with weapons of mass destruction, that deal with human rights. . . . So this will continue on for another couple of months, right until the end.”

The confrontation with Iran is the unpredictable X-factor in national security. Until Inauguration Day, the danger of a U.S. or Iranian strike remains on the table — a small but still real possibility. Starting a war without provocation is never wise, but especially not for a divided country on the verge of political transition.