WASHINGTON – At midnight on July 13, 2015, fortified for their 18th sleepless night, journalists in Vienna were put on notice: A landmark deal governing Iran’s nuclear program was finally at hand.

The White House had taken several days quietly preparing for this moment. They knew what was coming: A fanfare announcement of the Joint Comprehensive Plan of Action (JCPOA) to govern Iran’s nuclear program, with a ceremony in Austria and complementary televised speeches from US President Barack Obama and Iranian President Hassan Rouhani.

Those events would swiftly be followed by a relentless onslaught of political opposition in the form of ads, of money, of Prime Minister Benjamin Netanyahu.

Israeli and American officials now say open conflict between their governments was inevitable, and compare the 2015 crisis to an unstoppable train bound for a crash. That train left its station of origin back in 2011, when a back channel first opened with Iran in Oman; but it was in 2015 when the effects of the US-Israel crisis were most acutely felt, when the public first began to truly understand why the two governments so dramatically diverged.

The White House long knew why Israel opposed not any nuclear deal with Tehran but – from its point of view – any achievable deal: any agreement that Tehran would actually go along with. The Obama administration understood that Israel sought to deny Iran the strategic benefits of a nuclear program vast and efficient enough to secure Tehran as a nuclear weapons-threshold state. That standard was never shared by the administration; Iran is and will always be a threshold state, US officials privately say, and preventing them from acquiring the weapon itself is all the US could reasonably do.

And yet the Israeli government saw a systematic breakdown of a position based, from its point of view, in moral authority and practical strength: A willful surrender of the high ground by the US to accept Iran as a threshold state, and a decision by the president not to reflect Israel’s position in talks to which they were not directly a part.

Two years of private negotiations between American and Israeli officials on the sidelines of the nuclear talks began with deep distrust: Israel was kept in the dark when the talks first began, and learned of them not through US-Israeli defense cooperation, but by spying on the comings and goings of unmarked US government planes in Muscat.

As talks proceeded without Israel’s priorities reflected in Washington’s negotiating position – a posture US officials defend to this day, arguing that Netanyahu’s idea of a deal was Iran’s total capitulation – the Israeli government, in 2015, came to the conclusion that it had no choice but to bring its argument to the public.

The prime minister’s pivotal speech to the US Congress in March, to him and his aides, was ultimately the product of those failed private efforts to get the Obama administration to represent Israel’s position in the nuclear negotiations. Israel had no choice, its political class determined, but to speak out publicly, and loudly.

So on July 13, the White House was prepared for what would come next from Jerusalem. The announcement would come the following day; but in the meantime, officials set up a basement office that would serve as a war room against opponents – Democrats and Republicans alike.

Top officials, the president included, would lobby congressmen on an individual basis as they never had before. A special Twitter account would push the White House narrative, told elegantly and confidently on a special White House website explaining the benefits of the JCPOA.

Israel’s policy to go public – which debuted with leaked details of the deal by Israeli officials to The Jerusalem Post in November 2014 – set the stage for a yearlong feud unlike any other in the history of the alliance.

Now entering a new year, with implementation of the deal all but assured, data suggest the product of that feud was a sharpening partisan divide in the US over Israel, over its leadership and its role in American politics.

A poll released by the Brookings Institution’s Center for Middle East Policy in December found that unfavorable views of Netanyahu among Democrats increased sharply from 22 percent in 2014 to 34% in 2015.

While Netanyahu is the world’s most admirable leader amongst Republicans – tied with the late Ronald Reagan – he barely registers with Democrats, only 18% of whom view him favorably.

After debate over the nuclear deal gripped Congress in September, now precisely half of Democrats say Israel has too much power over American politics.

Israel’s government points to different figures: Over half of Democrats are either wary or disapprove of the nuclear deal, according to Pew Research Center polling, and a definitive majority of the American electorate as a whole disapproves. Americans now consider Iran’s nuclear program even more of a threat to the well-being of the US than they did a year ago.

The great divergence over Iran of 2015 will have a direct effect on the year to come for these reasons: The moment, like few in modern times, provided the American people with a policy contrast between the US and Israel on a matter of importance to both peoples. When Americans go to the polls, 59% say that a candidate’s position on Israel will matter to them.

At a forum hosted by Brookings last month, Hillary Rodham Clinton, the likely Democratic nominee for the presidency in 2016, spoke on these trend lines, emphasizing her personal commitment to Israel while warning of a growing generational divide.

“With every passing year we must tie the bonds tighter, reach out to the next generation to bring them with us and do the hard necessary work of friendship because there is a new generation in both countries today that does not remember that shared past,” she said to the think tank in Washington on the first night of Hanukka.

“Young Americans who didn’t see Israel in a fight for survival again and again,” she continued, “young Israelis who didn’t see the United States broker peace at Camp David or kindle hope at Oslo or stand behind Israel when it was attacked – they are growing up in a different world and the future of our relationship depends on building new ties for a new time.”

The policy effects of the JCPOA, secured in a tumultuous year of diplomacy, will be felt in precisely eight years with regard to centrifuge and ballistic missile development; in 10 years with regard to the efficiency and size of Iran’s nuclear infrastructure; in 15 years or longer for some other provisions, including key international requirements on transparency and access. It will be felt in short order as Israel monitors the development of Sunni nuclear programs and the strengthening of Shi’a proxy armies regionwide.

The political effects in the US will be immediate. Fallout from the fight in 2015 will have long coattails, sure to shape the most important decision of all for the fate of the nuclear deal: the next occupant of the Oval Office and guarantor of the unsigned nuclear pact.