Washington DC, United States - US Congressman Joe Crowley laughed out loud when House Republicans attempted - and failed - to block President Barack Obama's agreement to ban Iran from gaining nuclear weapons.
"You're going to need a lot of psychiatric couches to deal with that issue," Crowley, a leading Democrat, guffawed.
To most Europeans, the agreement reached between Iran and the US, France, Germany, UK, Russia, and China is solid. As a technical, non-proliferation protocol, it was widely endorsed by nuclear scientists and hailed as a model for the future.
So why would a deal with Iran - which many diplomats believe will open a new door to regional progress in the Middle East - engender such controversy in the US?
RELATED: The Iran deal is good for Middle East peace
It's an important question since the deal is now an important issue in the US presidential campaign, with top Republican candidates pledging to undo it. At stake is the future of US global leadership, according to lawmakers, deal advocates, and analysts.
| Obama faces opposition in Congress over Iran deal
"Here you have what is ... a very solid agreement with Iran that ... could have gotten rejected in a way that would have been very detrimental for US and global security. It's not rational," Tom Collina, policy director at the Ploughshares Fund, which supports the deal, told Al Jazeera.
Republican front-runner, Donald Trump, speaking to a Tea Party rally against the nuclear deal at the US Capitol last week, called the agreement "incompetently negotiated" by "very, very stupid people" in the Obama administration.
Iran's leaders, Trump said, "rip us off [and] take our money; they make us look like fools", and threaten Israel's future.
Indeed, this kind of emotive, anti-deal rhetoric has been effective among Republican voters.
The powerful pro-Israel lobby, AIPAC, spent $20m on TV ads and social media depicting mushroom clouds from nuclear explosions next to an evil-looking ayatollah. Israeli Prime Minister Benjamin Netanyahu made an aggressive play to undermine the US president.
"What happened, though, is something interesting, and that is that the Republican rhetoric did sour the Republican rank and file. Public opinion among Republicans, in general, became much more opposed to the deal than the case was last spring," Shibley Telhami, a pollster and professor at the University of Maryland, told Al Jazeera.
RELATED: Iranian Americans bank on historic nuclear deal
But most Democrats and independents remained supportive, and when votes were cast, only narrow bipartisan majorities opposed the agreement.
Rules in the US Senate protect the minority party from being overridden by the majority, meaning Senate Republicans would need at least six Democrats to agree with them. They got four.
In any case, to actually stop US participation in the P5+1 deal, they would have needed 13 Democrats to override a potential presidential veto.
The Republican opposition represents a "regression" from the US' post-World War II world leadership role that stems from the "fear of foreigners, fear of the unknown, fear of giving up sovereignty", Democrat Senator Richard Durbin, told Al Jazeera.
"It's a serious mistake," Durbin said. "We live in an interconnected world on so many different levels that if we don't deal with these international institutions, then we're not dealing with the reality of the world today."
Medea Benjamin, co-founder of pro-peace group CodePink, said Republican opposition to the nuclear deal reflects a refusal to recognise the limits of US power.
"Much of it comes down to thinking that the US has the right because we are the exceptional, great country, and we have the ability - because we have this military might - to shape the world in the way we think fits," Benjamin told Al Jazeera.
Taking a hard line
To be sure, Iran's Ayatollah Ali Khamenei's statements are often interpreted in the US as hostile and give Republicans and a number of pro-Israel Democrats ample material to make a case against the agreement.
As Congress was voting, Khamenei issued a statement appearing to rule out additional negotiations with the US on regional issues, and again, calling the US "the Great Satan", while espousing a view that Israel "will not survive" 25 years as a "Zionist regime".
RELATED: Iran deal does not mean peace in the Middle East
"The European perspective, going back to Neville Chamberlain, is a perspective which is always to advance diplomacy and compromise," said Ed Royce, Republican chairman of the House Committee on Foreign Affairs, who is now leading a Republican legal manoeuvre to block the Iran deal in US courts.
"At this point in time, the ayatollah is not saying 'death to Berlin', 'death to London', 'death to Paris'," Royce told Al Jazeera. "He is saying 'death to America' and 'death to Israel'. So for us here in the United States, who are chastised as being the 'Great Satan', that communication resonates."
| Iran nuclear deal: How both sides tell the story
For Democrats, the Iranian commentary looks like bluster. So they tend to focus instead on the actual terms of the agreement and its implementation, including the declaration that Iran will never seek a nuclear weapon, amid permanent monitoring and inspection by the UN's International Atomic Energy Agency.
Democrats view the Republican opposition as another example of a partisan campaign to undermine Obama that had been waged since he was first elected in 2008.
Republicans in Congress have voted symbolically more than 50 times to repeal the Affordable Care Act, Obama's signature domestic policy achievement.
"It is an antipathy that they have for the president; it is partisan in nature. It's sour grapes in many respects," Crowley told Al Jazeera. "They have worked since day one to make him ineffectual, and it's no surprise that, by the second-half of the second term of a president, these kinds of [international] deals come about. They were never poised to support him."
In the end, the American public is likely to back the deal despite ambivalence and concerns about aspects such as lifting the UN embargoes on the sale of conventional arms and intercontinental ballistic missile technology to Iran, Telhami said.
"It is not true the public has soured against the deal. By and large, a slight majority of Americans still support the deal."
Source: Al Jazeera