WASHINGTON—With the midterms over, President Trump’s advisers and foreign allies have been racing to shape his decision on whether to end the Iran war or reignite it.

Voters soundly repudiated the war at the ballot box, then Vice President JD Vance questioned whether it was worthwhile on social media. Before that post, Vance told the president that he intended to blame the defeat on the war, U.S. officials said.

Another camp, which includes Defense Secretary Pete Hegseth and U.S. Central Command chief Adm. Brad Cooper, have supported a return to major combat operations during recent briefings on military options, U.S. officials said. Several hawkish outside advisers have called Trump since Election Day to make the case that his legacy depends on forcing Iran to surrender its nuclear program, which would allow the president to boast the political sacrifice was worth the cost, U.S. officials and another source familiar said.

Secretary of State Marco Rubio and Treasury Secretary Scott Bessent have advocated for tightening sanctions and continuing the blockade on Iranian trade. Special envoy Steve Witkoff, like Vance, has sought Trump’s continued backing for diplomatic efforts for a deal to end the war and reopen the Strait of Hormuz, officials said. And other outside advisers have also called Trump with the message that it is time to end the war.

Israeli Prime Minister Benjamin Netanyahu, meanwhile, is still pushing for renewed strikes. Gulf allies are more skeptical. Qatari officials said Friday they had launched an 11th-hour attempt to stave off a new American operation and bridge the gaps between the two warring parties to open the Strait of Hormuz and lift the U.S. blockade. “Our mediators are working as we speak to avoid another wave of escalation in the region,” said Qatari Prime Minister Sheikh Mohammed bin Abdulrahman al-Thani at an event in Oxford, England.

Qatari ruler Sheikh Tamim bin Hamad al-Thani spoke with President Trump on Friday, and Gulf officials said there were signs that both sides were looking for an off-ramp.

Iranian officials are set to return to Doha, Qatar, in the coming days, possibly as early as Saturday, to discuss the prospective deal, the officials said.

Gulf foreign ministers have been attempting to arrange either a call with Trump or a high-level meeting in Washington to make the case for a deal, people familiar with the discussions said.

According to the people, the deal under discussion would shrink the timetable for preliminary talks from 60 days—the term of the June memorandum of understanding—to two days, to move almost immediately into nuclear negotiations. One of the people said that could give Trump a face-saving way to begin to wind down the war. It is unclear whether Iran would accept such a deal.

The deliberations show Trump at the precipice of a fateful decision, one that could dictate the course of his remaining presidency, but this time without the safety nets of a united team or a favorable political climate.

“Now we will make a decision,” Trump told reporters on Thursday. “I would rather not destroy the rest of the country if possible, but maybe I will have to. You’ll know soon enough.”

Explosions were reported on Qeshm Island in the Strait of Hormuz on Friday evening after what a U.S. official described as small-scale strikes. The U.S. has conducted several such strikes in recent weeks while cautioning that they didn’t signal a return to full-scale combat operations.

“The Democratic success in the midterms exacerbates the predicament facing the president,” said Suzanne Maloney, an Iran expert and foreign-policy vice president at the Brookings Institution. The options available to Trump “will likely only compound the strategic and economic price that Americans have already paid.”

No course is without risk, officials have told Trump. Iran is threatening to expand its retaliation beyond the Middle East if attacked. But if Trump signals an intention to get out, Tehran could extract greater concessions in talks or push for a seizure of the Strait of Hormuz.

The disagreements and conflicting counsel have made a difficult decision all the more wrenching for Trump, whom officials said has toggled since Tuesday’s returns between dismissing the electoral rebuke and feeling chastened by it. Trump has yet to definitively signal what he will do, often expressing a desire for diplomacy and fresh attacks in the same breath.

Speaking to reporters this week, Trump said he had “no choice” but to suffer the political cost to target Iran’s nuclear program. “If I had to do it again, I’d have to do it again, because, long term, it’s the only answer.”

A White House official said Trump is in no hurry to make a decision as the Iranian economy sputters and oil flows through the Strait of Hormuz. Trump will ultimately make the best decision for the U.S., the official said.

A Pentagon official said the department’s job is to develop and execute military options for the president.

Should Trump listen to those advising him to “finish the job,” the Pentagon stands ready to execute his orders swiftly, U.S. officials say. However, the ideal time frame to resume operations begins later this month when additional equipment arrives in the Middle East, the officials said.

The USS Theodore Roosevelt carrier strike group, armed with dozens of jet fighters, is steaming toward the region from the Pacific. But it will spend a few days in Singapore starting on Friday for a port call and isn’t expected to arrive in the Middle East for at least another two weeks, according to a U.S. official.

Meanwhile, an additional Marine expeditionary unit is also expected to join the armada of roughly 20 other ships already operating in the region later this month, officials said. The U.S. has moved a Patriot air-defense system to Israel, relocated personnel away from bases considered vulnerable to Iranian retaliation, and deployed additional ships, munitions and troops to the region.

Hegseth and Cooper have spent weeks making preparations for major combat operations. They have advised Trump that resuming attacks—this time targeting Iranian energy infrastructure, nuclear facilities and missile and drone arsenals—is the only way to make Iran surrender its nuclear material, U.S. officials said.

But some experts say it isn’t clear that additional strikes will force Iran into a deal, especially after the regime has survived eight months of war. Behnam Ben Taleblu, a senior fellow at the Foundation for Defense of Democracies think tank, said he thinks Trump should “hold the line,” allowing time for sanctions and the blockade to work.

“I think the president at this moment in time does have a winning hand, and that winning hand will put the onus of escalation or engagement on the Islamic Republic,” he said. “The benefits of a conflict relative to how little Iran has been able to rebuild pale in comparison to the costs of a conflict that would be felt economically and politically.”

There are lingering questions about how long Hegseth will be in the Pentagon’s E-Ring and the Situation Room. White House officials and Republican lawmakers have begun pointing fingers at Hegseth, The Wall Street Journal reported, blaming him for convincing Trump that the Iran war would be over in a few weeks. Trump says he maintains full faith in Hegseth, while Pentagon spokespeople say the secretary expects to be in his position through the remainder of the administration.

If Trump pushes for a peace deal to end the war, he will likely find Iranian counterparts less willing to make the concessions he wants. “Their price tag is considerable,” said Gregory Brew, an Iran expert at the Eurasia Group consulting firm. Tehran aims for a return to this summer’s “memorandum of understanding,” which allowed the regime to sell oil on the open market again, and fully reopen the strait before any discussions about its nuclear program, he said.

Maintaining the status quo—sanctions and the blockade—could prove attractive and the path of least resistance for the president, Brew added, “but it also means that Trump commits to continuing the war for the foreseeable future, with oil prices remaining high and Iranian attacks in the strait the new normal.”

While the president signals confidence, the conundrums presented by any of the three pathways and the continuing debate provide Trump with no clear upside.

“What do you choose that is the least bad option?” asked Seth Jones, president of the Defense and Security Department at the Center for Strategic and International Studies think tank.

Write to Alexander Ward at alex.ward@wsj.com, Lara Seligman at lara.seligman@wsj.com, Benoit Faucon at benoit.faucon@wsj.com and Natalie Andrews at natalie.andrews@wsj.com