WASHINGTON — Many factors are to blame for the dying prospects of reviving the 2015 Iran nuclear deal. But perhaps nothing has hobbled the Biden administration’s efforts more than the legacy of President Donald J. Trump.

It was Mr. Trump, of course, who withdrew in 2018 from the nuclear pact brokered with Iran by the Obama administration, calling it “the worst deal ever.”

But Mr. Trump did more than pull the plug. U.S. officials and analysts say his actions vastly complicated America’s ability to negotiate with Tehran, which has made demands outside the nuclear deal that President Biden has refused to meet without receiving concessions.

The original pact limited Iran’s nuclear program in exchange for the easing of economic sanctions that have crushed the country’s economy. After Mr. Trump quit the deal and reimposed sanctions, Iran also began violating its terms.

With no compromise on a new agreement in sight and Iran making steady progress toward nuclear capability, the Biden administration could soon be forced to decide between accepting that Iran has the capacity to make a bomb or taking military action to prevent it from doing so. Iran maintains that its nuclear program is for peaceful purposes, like producing medical isotopes to diagnose and treat disease.

Mr. Trump handed Mr. Biden a needless nuclear crisis, Robert Malley, the State Department’s chief negotiator, told senators at a hearing late last month, adding that the chances of salvaging the deal had become “tenuous.”

Negotiations in Vienna to restore the deal have been on hold since mid-March. On Monday, Secretary of State Antony J. Blinken said Iranian leaders “have to decide, and decide very quickly, if they wish to proceed with what has been negotiated and which could be completed quickly if Iran chose to do so.”

This month, after the United States and European allies criticized Iran for failing to cooperate with international inspectors, officials in Tehran doubled down by deactivating and removing some surveillance cameras in its nuclear facilities.

Mr. Blinken said Iran’s move was “not encouraging.”

On Tuesday, Iran’s foreign minister, Hossein Amir Abdollahian, said Iran had proposed a new plan to the United States, but he did not provide any details.

“Iran has never run away from the negotiating table and believes negotiations and diplomacy is the best path to reaching a good and lasting deal,” he said in Tehran.

A senior administration official in Washington who is close to the negotiations said he was unaware of any new proposal from Tehran but “of course we remain open” to ideas that might lead to an agreement.

Mr. Trump’s legacy haunts the talks in at least three notable ways, according to several people familiar with the negotiating process, which Mr. Biden began early last year.

First, there was what the Iranians call an enormous breach of trust: Mr. Trump’s unilateral withdrawal from the deal, despite Iran’s adherence to its terms, confirmed Tehran’s fears about how quickly the United States can change tack after an election.

At the negotiating table in Vienna, the Iranians have demanded assurances that any successor to Mr. Biden be constrained from undoing the deal again.

In late February, 250 of 290 Iranian parliamentarians signed a letter to Iran’s president urging him to “learn a lesson from past experiences” by “not committing to any agreement without obtaining necessary guarantees first.”

Biden administration officials have explained that is not possible, given the nature of America’s democratic system. (Nuclear negotiations between world powers and Iran began under President George W. Bush and were finalized in the 2015 deal in a commitment made by President Barack Obama. The agreement was not ratified as a treaty by the U.S. Senate.)

The Iranians have a related concern: Foreign companies may be reluctant to invest in Iran if they believe that America’s sanctions hammer might fall again after the next presidential election.

Mr. Trump created a second major hurdle for restoring the deal by heaping around 1,500 new sanctions designations on Iran. Iran has insisted that those sanctions be reversed — none more so than Mr. Trump’s 2019 designation of Iran’s elite Islamic Revolutionary Guards Corps as a terrorist group. Previous administrations have condemned the Revolutionary Guards, which oversee Iranian military proxies in Lebanon, Syria and Yemen and have aided insurgents in Iraq who killed Americans. But they were wary of identifying an arm of a foreign government as a terrorist group.

Iranian negotiators have said that, to clinch a renewed nuclear agreement, Mr. Biden must drop the Revolutionary Guards’ terrorist label. But Mr. Biden has refused without Iran first giving other concessions — and Mr. Blinken described the group as a terror organization as recently as April.

Some analysts call the matter largely symbolic, but potently so. The United States had already heavily sanctioned the Revolutionary Guards and the group’s commanders, and the impact of the penalties was expected to have long-term consequences for Iran’s economy. Yet the U.S. Senate approved a nonbinding resolution by a 62-to-33 vote in May prohibiting Mr. Biden from removing the designation. Some key Democrats supported the measure, including Senator Chuck Schumer of New York, the majority leader. Prime Minister Naftali Bennett of Israel wrote a message of approval on Twitter after Mr. Biden informed him that the designation would stay.

The senior administration official said the United States had been open to lifting the terror designation, but only if Iran was prepared to offer new assurances about security concerns related to the Revolutionary Guards. The official, who spoke on the condition of anonymity to describe the private negotiations, would not be more specific except to say that Iran had refused to cede any ground.

People familiar with the talks point to a third, logistical way in which Mr. Trump’s legacy looms: Iranian officials have refused to speak directly to American officials since Mr. Trump’s exit from the deal. (Mr. Trump further enraged Iran by ordering the assassination of a senior Iranian military commander, Qassim Suleimani, in 2020.)

During the talks in Vienna, Mr. Malley communicated with Iranian negotiators by sending messages through European intermediaries from a hotel across the street. That bogged down the process and occasionally made for time-consuming misunderstandings.

Trump administration officials and their associates expected such complications, to varying degrees, as they crafted a policy meant, in part, to make any future negotiations difficult without dramatic changes in Iran’s behavior.

Mark Dubowitz, the chief executive of the Foundation for Defense of Democracies, a Washington think tank that takes a hard line against Iran’s government, was an outside architect of what he described in 2019 as a “wall” of Trump administration sanctions against Iran, including the terrorist designation of the Revolutionary Guards.

“I’m gratified that the sanctions wall has basically held, because it should hold,” Mr. Dubowitz, who strongly opposed the nuclear deal, said on Monday. “Iran should not get sanctions relief unless it stops the underlying behavior that led to the sanctions in the first place.”

Biden administration officials say that Mr. Trump made maximalist demands of Iran that were unrealistic, even given the intense economic pressure Mr. Trump applied on Tehran.

The Trump administration “predicted that Iran would not restart its nuclear program, and that Iran would come to negotiate on our other concerns,” Mr. Malley said at the Senate hearing. “I wish they’d been right. Regrettably, they were proven wrong on all counts.”

Iran began increasing its nuclear program after Mr. Trump withdrew from the deal. But Mr. Dubowitz said it accelerated its uranium enrichment to more dangerous levels and took other threatening steps after Mr. Biden made clear that he was eager to return to the 2015 agreement.

Dennis Ross, a Middle East negotiator who has worked for several presidents, said both sides still had incentives to compromise.

Iran’s supreme leader, Ayatollah Ali Khamenei, needs sanctions relief for his economy. As for Mr. Biden, Mr. Ross said, “he doesn’t have any other way at this point to limit the Iranian nuclear program — and it is marching ahead right now” with less monitoring by the International Atomic Energy Agency.

Mr. Ross acknowledged that a nuclear deal that had limited support in Congress even in 2015 looked less appealing today, now that Iran has acquired more atomic know-how and the agreement’s key “sunset clauses” are set to expire in just a few years. But he said Mr. Biden still might want a return to the deal “not because he thinks it’s so great, but because the alternative is so bad.”

“Otherwise,” he said, “the Iranians can just keep pushing ahead.”

Farnaz Fassihi contributed reporting from New York.