The war in Iran is deeply unpopular with Americans. Recent polls indicate as many as two-thirds of voters disapprove of President Trump’s handling of the eight-month conflict, which has driven up prices and depleted U.S. ammunition stockpiles.

Yet in the final days of the campaign, Mr. Trump kept talking about it.

“We still have to take care of, I would say, one or two sites, but we can do that in 10 minutes,” he told reporters on Saturday.

“The only reason we’re not finished with Iran is, I want to be nice, I want to try and save all those lives if I can,” he said at a campaign rally on Sunday.

“We had a war with Iran,” he added Monday. “We won.” Hours later, officials confirmed that the U.S. military had struck Iran’s Qeshm Island in what they described as a defensive measure that was not expected to escalate.

Here are three reasons why Mr. Trump kept bringing up Iran, according to analysts.

To push Iran toward a deal

Mr. Trump, who prides himself on his deal-making, could be trying to restart talks.

“By threatening strikes, he wants to send the Iranians a message: ‘Come to the table now or else,’” said Arta Moeini, managing director of the nonpartisan Institute for Peace and Diplomacy, which advocates for military restraint.

Iran’s foreign ministry on Monday said it was prepared to reopen the Strait of Hormuz in two days if the United States agreed to several demands, including lifting U.S. economic sanctions against Iran and releasing billions of dollars in frozen Iranian assets.

The Trump administration is unlikely to accept either condition. For now, Mr. Trump “is going to use the promise of diplomacy again, as he has done before,” Mr. Moeini said. “He can announce that, and maybe get better results for the election, but still later say, ‘They didn’t do what they promised to do, and so we can attack.’”

A family having dinner at home in Tehran on Sunday as television news reports on negotiations between the United States and Iran.Credit…Arash Khamooshi/Polaris for The New York Times

‘Tough guy’ rhetoric has worked before

Threatening rhetoric is part of Mr. Trump’s brand and has helped him build a loyal following.

“There is a very real strand of American public opinion, the Jacksonian tradition, that likes a leader who projects toughness and who is prepared to whack the bad guys,” said Andrew Payne, a research director at Chatham House, a policy institute in London.

But Mr. Payne called that approach to Iran a “misguided” political strategy. “You’ve seen the polling,” he said.

He sees Iran as a legacy issue

Yet polling will matter less for Mr. Trump going forward. Regardless of the outcome of Tuesday’s elections, he will be entering his final two years in office, a period when presidents often take policy risks to secure their legacies.

“He has staked his legacy in foreign policy, to some degree, on Iran,” Mr. Payne said. “It’s more important for him to try and get some favorable resolution to that in the long term than worrying about the short-term impact at the polls.”

The Trump administration is already moving three aircraft carriers, thousands of Marines, fighter jets and Special Operations forces to the Persian Gulf region, to be ready to strike within days.

“I do believe that he will escalate no matter what,” Mr. Moeini said. “I don’t think that’s cheap talk.”