It was slammed by presidential candidates, leading conservative thinkers and GOP members of Congress, who invited Israeli Prime Minister Benjamin Netanyahu to deliver a blistering attack in an address to Congress. And in the month afterward, as Capitol Hill weighed whether to endorse it, Republicans -- and some Democrats -- lobbied fervently against it.
They narrowly lost at the time, but they promised to make it a major campaign issue. The GOP saw a political opening in polls showing the American public opposed the deal -- which lifted U.S. sanctions on Tehran in exchange for curbs on its nuclear program -- and the key diplomatic role Democratic presidential candidate Hillary Clinton played in the Obama administration.
But in the intervening months, the issue has largely dropped off the political agenda. While GOP presumptive nominee Donald Trump regularly rails against the deal on the campaign trail, international challenges like global terror, China and Russia have gotten more attention and had a greater impact on the political environment.
Criticism of the deal has "toned down quite a bit from the period of congressional review last summer," noted Robert Einhorn, a former State Department adviser involved in negotiating the deal.
The Republican convention next week presents another platform for GOP attacks on Iran, but if the months since the pact started to be implemented in January is any guide, the issue is unlikely to gain increased political traction.
The reasons, according to Washington insiders and policy experts, have largely to do with Donald Trump and Hillary Clinton.
Trump, despite his repeated criticism of the deal, hasn't given a detailed takedown of its shortcomings or offered a substantially different approach -- in fact, he was one of the few Republican candidates who didn't call for ripping up the accord once the White House changed hands.
And the Republican Party, riven with internal divisions and trying to articulate a clear foreign policy as Trump pulls it toward isolationism, hasn't developed the concentrated campaign a nuanced international issue can demand.
At the same time, Clinton managed to position herself as more hawkish than President Barack Obama on Iran policy while claiming credit for the diplomatic groundwork on sanctions and secret diplomacy that brought Iran to the table -- without having been involved in the contentious nuclear negotiations themselves.
Backers of the Iran deal say that's been particularly helpful since the agreement has so far held. It's another reason they think it hasn't been in the political limelight.
Secretary of State John Kerry marked the anniversary in Paris Thursday, telling reporters "one year later, a program that so many people said will not work, a program that people said is absolutely doomed to see cheating and be broken and will make the more dangerous, has, in fact, made the world safer."
President Barack Obama echoed Kerry's sentiment, issuing a statement that "the Iran Deal has succeeded in rolling back Iran's nuclear program, avoiding further conflict and making us safer."
"Opposition has been toned down because it is very clear that Iran's nuclear infrastructure has been sharply reduced," Einhorn told CNN.
He added that there was "no evidence" of Iranian violations, a statement expressed by the State Department in a briefing last week.
"The nuclear aspects of the deal are working very well," agreed Barbara Slavin, director of the Washington-based Atlantic Council's Future of Iran Initiative.
Einhorn, now with the Brookings Institution, said the reduced criticism also stems from an unlikely source: Israel.
He noted that former officials, including the head of Israel's top spy agency, have come out in favor of the deal.
And Netanyahu's former minister of defense, Moshe Ya'alon, seemed to acknowledge the deal was working in June.
Iran's nuclear program "has been frozen in light of the deal signed by the world powers and does not constitute an immediate, existential threat for Israel," he said at a policy conference in Israel.
However, there have been plenty of dissenters and problematic developments that GOP opponents might have seized on more forcefully.
A UN Secretary General report obtained by Reuters last month found that Iran was violating "the spirit" of the Iran deal and German intelligence released a report saying Iran had continued to seek illicit nuclear-related technology in 2015, as the deal was being negotiated. Neither reignited the political firestorm that accompanied the deal's announcement.
Even once-unthinkable praise of Iran from top U.S. officials -- Secretary of State John Kerry in Aspen in June called Iran's efforts to fight ISIS in Iraq "helpful" -- have failed to generate significant controversy.
While Trump often blasts the deal in his stump speeches, saying Iran "made such fools of us," he has rarely made the deal or U.S.-Iran relations a central theme.
"The reality with Trump is he hasn't talked a lot about foreign policy," said Mark Dubowitz, executive director of the Foundation for the Defense of Democracies.
Dubowitz, an opponent of the nuclear deal, added that the intense media coverage of Trump and the presidential campaign was also part of the reason the Iran nuclear deal has not continued to get a lot of attention.
All the discussion around Trump has "sucked the oxygen out of the debate," leaving little room to talk about Iran, he said.
There's also the way in which the Democratic Party's standard bearer, former Secretary of State Hillary Clinton, has managed to largely shield herself from the political ramifications of the deal.
Clinton was involved with sanctioning Iran but left the administration "before the productive phase of negotiations began in 2013," according to Einhorn.
She has done an "effective job of insulating herself on the charge she would be weak on Iran," Dubowitz said, noting that she's appeared more skeptical of Iran than Obama has -- a position he labeled "partly political" and "partly who she is."
Slavin, too, thinks that Clinton's position on Iran helps protect her from criticism of the deal.
"She is much more hawkish-sounding on Iran than Obama is," she said.
But while the volume of criticism of the deal might have decreased, experts believe that it will continue.
Much of the political battle has shifted to Congress, where, Dubowitz maintained, "opposition has intensified."
He cited over 30 pieces of legislation pending in Congress pertaining to sanctioning Iran on a variety of issues.
One area of contention involves the proposed sale of Boeing aircraft to Iran's state airline. Previously the carrier had been designated as an arm of the Iranian military -- a designation that was withdrawn after the signing of the deal. Some members of Congress are seeking to block the Boeing sale because of Iran's continued support of Bashar al-Assad's government in Syria.
But Einhorn and Slavin argued that such support -- and the host of other bad behaviors Iran has exhibited in the past year -- weren't directly addressed in the nuclear agreement and therefore should not form the basis of criticism of that accord.
They include Tehran's jailing of American-Iranian dual nationals, seizure of American sailors who had strayed into Iranian waters, ballistic missile activity and its continued role as a state sponsor of terrorism.
Still, Einhorn said, "Because this is an election year, the resistance will stay alive."