America’s Christian Zionists are on a roll. In December, they scored a major political victory with President Trump’s announcement recognizing Jerusalem as Israel’s capital and initiating the relocation of the U.S. Embassy there. In March, evangelical supporters of the Jewish state notched another win with the inclusion of the Taylor Force Act in an omnibus spending bill. The act makes certain funding to the Palestinian Authority conditional on the PA cutting stipends to families of dead or incarcerated terrorists.

But their latest victory — Trump’s announcement that he is withdrawing the United States from the Iran deal (the Joint Comprehensive Plan of Action, or JCPOA) and reimposing sanctions against Iran that the deal had lifted — could have dramatic geopolitical consequences. Though shocking, the president’s decision has long been expected. After lobbying Trump vigorously in support of the deal during a state visit to the White House last month, French President Emmanuel Macron left convinced the president would withdraw from the JCPOA “for domestic reasons.”

What are those domestic reasons? One of the main reasons is also the most overlooked: Many among Trump’s most loyal backers, white evangelicals, have demanded it. Evangelical supporters of Israel have long been among the leading domestic opponents of the Iran deal. The same organizations that lobbied for the Jerusalem move — including both Christians United for Israel (CUFI) and American Christian Leaders for Israel — lobbied against the JCPOA when it was being negotiated and have called for its renegotiation or reversal ever since. They have also agitated for the appointment of the deal’s opponents to the administration, such as new Secretary of State Mike Pompeo.

Why have Christian Zionists opposed the deal? It is not simply a desire to bring on the apocalypse, as some critics have charged. While some evangelicals see Iran as a central actor in various End Times scenarios, most Christian Zionists are motivated by a more basic belief that Jews remain God’s chosen people and that Christians should support the world’s only Jewish state. More specifically, many believe God will bless those nations that “bless” Israel and curse those nations that “curse” it, a belief rooted in Genesis 12:3.

For Christian supporters of Israel, opposing the JCPOA has provided an opportunity to bless Israel or — perhaps more accurately — to avoid cursing it. Of course, Genesis 12:3 does not on its own suggest a particular stance on the JCPOA. But a half-century of developments in the United States and the Middle East have convinced Christian Zionists that the JCPOA poses a threat to Israel, which, in turn, means that supporting it would run afoul of the biblical teaching.

JCPOA is designed to prevent the Iranian government from obtaining nuclear weapons. But Christian Zionists fear that it will fail, believing that the Iranian government remains committed to pursuing nuclear weapons either in violation of the agreement or shortly after it “sunsets.” As Iranian leaders have repeatedly threatened Israel’s destruction, the implications of a nuclear Iran seem clear. To Christian Zionists, this is not just overheated rhetoric — it’s an existential threat to the Jewish state.

They also worry that the JCPOA does not address Iran’s material support for Israel’s enemies, especially Hezbollah, a longtime client of Iran that has harassed Israel from southern Lebanon since the early 1980s, and Hamas, which has initiated repeated rounds of rocket attacks against Israeli population centers since seizing control of the Gaza Strip in 2007. Indeed, Christian Zionists argue that the JCPOA’s sanctions relief has actually allowed Iran to increase funding to both groups (an argument Trump seemed to parrot in his speech announcing U.S. withdrawal from the deal).

Coloring these assessments are relationships forged between conservative evangelicals in America and the Israeli government since the 1967 Six-Day War. Over the past half-century, Israel has actively worked to build alliances with American evangelicals, a process that intensified after the conservative Likud Party first came to power in 1977.

These bonds mean that Christian Zionists take seriously the warnings about the JCPOA from their Israeli allies, including Prime Minister Benjamin Netanyahu. And Netanyahu has relentlessly sounded the alarm about the dangers posed by Iran and the JCPOA. Just last week, he held a dramatic presentation of documents obtained by Israeli intelligence that purported to show Iran had misled the international community on its nuclear program. Within hours of the presentation, CUFI was circulating talking points about the presentation to its mailing list, claiming the documents “leave no doubt that the Iran Deal is fatally flawed.”

Even without the Israeli government’s prompting, though, Christian Zionists have long viewed Iran as an enemy. Since the establishment of the Jewish state, American Christian Zionists have understood the United States and Israel to be allies in an evolving series of civilizational clashes. Since the Islamic Revolution of 1979, many American evangelicals have come to view Iran as the embodiment, if not the architect, of this radical Islamic threat. In the dualistic worldview of Christian Zionists that pits Judeo-Christian civilization against “radical Islam,” the Iranian government cannot be trusted because it is intrinsically, religiously and — for some — demonically devoted to the destruction of both Israel and the United States.

Evangelical supporters of Israel often point to the Iranian leadership’s own religious rhetoric in making these points, noting in particular that Ayatollah Ruhollah Khomeini, the founder of the Islamic Republic, frequently denounced the United States as the “Great Satan” and Israel as the “Little Satan.” They also point to Iran and its clients’ very real struggle against American and Israeli interests in the Middle East — from the seizure of American hostages during the Islamic Revolution, to Hezbollah’s 1983 bombing of the U.S. Marine barracks in Beirut, to more recent proxy struggles in Iraq, Yemen and Syria. For Christian Zionists, Iran is an enemy that must be confronted, not negotiated with.

Netanyahu himself has skillfully played to these feelings in engaging American Christian audiences. In a video address to the CUFI annual summit last year, he proclaimed that the U.S. and Israel were engaged in “a struggle of civilizations … of free societies against the forces of militant Islam. The militant Sunnis led by ISIS, the militant Shiites led by Iran, they want to conquer the Middle East, they want to destroy the State of Israel, and then they want to conquer the world.”

Christian Zionists are celebrating Trump’s decision because they believe it will “bless” Israel. Whether that is true will only be evident once the implications of American withdrawal from the JCPOA become more clear. What is certain, though, is that when the new U.S. Embassy opens in Jerusalem next week, American Christian Zionists will have much more to celebrate than the Embassy itself — including their growing political heft in Trump’s Washington.