The rise of Donald Trump has terrified a lot of people around the world, and rightly so. But one person should be especially worried: Israeli Prime Minister Benjamin Netanyahu.

Trump, alone in the modern Republican Party, has tacked away from unconditional support for Israel. He has said he would take a "neutral" stance on the Israeli-Palestinian conflict, and suggested that if negotiations fail it might well be Israel's fault.

These comments don't reflect a fundamental challenge to America's Israel policy. Every American president has maintained neutrality on the Israel-Palestine conflict; each of the past three presidents has put pressure on Israel over the conflict.

Rather, Trump is challenging the way you're supposed to talk about Israel in the Republican Party. GOP presidential candidates have, for years now, felt the need to demonstrate unconditional support for Israel. While Trump's statements are in line with American policy, they're out of step with this traditional rhetorical requirement.

Trump, despite drawing attack from other GOP candidates on this issue, has paid no obvious electoral price for it. And that suggests Netanyahu could have a problem in Trump.

Netanyahu's core strategy for managing the US-Israel relationship depends on the GOP remaining a hard-line pro-Israel party, which he can rely while in power on to enact pro-Israel policies, and while out of power to pressure Democrats to tilt policy more in Israel's favor. This dynamic is particularly pronounced when it comes to the Israel-Palestine conflict and whatever pressure the US puts on Israel to find peace and end the occupation of the Palestinians.

Trump's success suggests that the GOP electorate may be only so committed to that position, as Haaretz's Chemi Shalev explains well in a recent column:

Exactly a year after Netanyahu took this logic to its extreme and stood on the podium of Congress as Leader of the Republican opposition to President Obama’s nuclear deal with Iran, the conception is falling apart. The notion that the Republican Party is a monolithic bastion of support that will withstand the test of time is evaporating. The belief that any Republican president who will follow Obama will be better for Israel is eroding with each passing day. Faced with the Trump phenomenon, Netanyahu’s Fortress GOP strategy is collapsing like a house of cards.

Trump's rise, and what it could portend for GOP politics and policies, suggests that Netanyahu's strategy for deflecting American pressure on the Israel-Palestine conflict may not be as foolproof as he'd hoped.

Netanyahu's "fortress GOP" strategy, explained

Benjamin Netanyahu is a right-wing Israeli politician who has long clashed with Democratic presidents. He believes, probably correctly, that Republicans would be less likely to pressure Israel into comprehensive peace negotiations, and more likely to take an aggressive approach to Israeli enemies in the region such as Iran.

So Netanyahu has formed a tacit alliance with the GOP, even though this comes at the expense of his relationship with Democrats.

When Netanyahu first ran for prime minister in 1996, Bill Clinton all but openly campaigned against him, inviting incumbent Prime Minister Shimon Peres to visit the White House just before the vote. Clinton thought Netanyahu's opposition to a Palestinian state would jeopardize peace negotiations. Netanyahu won anyway, resulting in constant tension in the US-Israel relationship until Netanyahu's defeat in 1999.

Netanyahu retook the premiership in 2009, and clashed with President Obama from day one on issues such as Iran and the peace process. Most famously, he conspired with Republicans to give to a major speech to Congress behind Obama's back, in March 2015, opposing the Iran nuclear deal.

This tension stems from a fundamental disagreement between Democrats and Netanyahu over policy — particularly his deep skepticism about the desirability of a Palestinian state. To counteract that, Netanyahu has pioneered a novel approach to Israel's relationship with the US: Ally with the Republican Party, and leverage overwhelming GOP support to defray the consequences of any conflict he has with Democrats.

Netanyahu has thought something like this for a long time. When Clinton was president, the prime minister built up relations with Speaker of the House Newt Gingrich and evangelical leader Jerry Falwell. In 2012, he practically endorsed Mitt Romney over Obama, to the point where clips of Netanyahu speeches were being featured in pro-Romney campaign ads.

This might seem odd, since historically both parties have been pretty friendly to Israel and presidents from both parties have pressured Israel on the occupation. But there's a difference in the kind of support you see within the parties. While Democrats generally have a positive view of Israel, Republicans overwhelmingly do — as you can see in the below chart:

Moreover, the nature of the two parties' support for Israel is different. Republicans favor uncritical support for Israel; they see its enemies as America's enemies, and see a Palestinian state as less important than Israel's security from terrorism. Democrats take a more measured view, diverging with Israel's right-wing leadership on the Iran deal and on the Israel-Palestine conflict.

You can see this divide in Gallup's latest poll data on US attitudes toward Israel: 58 percent of Democrats, but only 26 percent of Republicans, support establishing a Palestinian state today. Desiring a Palestinian state is not an anti-Israel position, of course, but it helps to make Democrats more likely to clash with Netanyahu, who in practice has tended to oppose a Palestinian state.

Why Trump challenges Netanyahu's strategy

A premise of Netanyahu's fortress GOP strategy is that Republicans will remain, for the foreseeable future, unconditional Israel supporters. Trump's rhetoric calls that into question. He is far from anti-Israel, but his willingness to be anything less than maximally pro-Israel, even if just in rhetoric, is a symbolic break.

The demographics suggest Trump could represent an even larger problem for Netanyahu's strategy.

According to political scientists, two forces make the GOP the hardcore pro-Israel party we know today. First is the rise of the religious right, which sees hard-line support for Israel as a religious obligation. Second is the neoconservative movement, which convinced most Republican leaders that being pro-Israel should be a core conservative value.

Trump is turning that conventional wisdom on its head. He has been winning with evangelical voters, for example, particularly with self-identified evangelicals who attend church less frequently.

This doesn't mean that evangelicals have suddenly softened in their support for Israel. But it does suggest that Trump offers them something — whatever theory of Trump's appeal you find most convincing — that is more powerful than their desire for a maximally pro-Israel candidate.

Meanwhile, neocons have united against Trump, most notably in an open letter vowing not to support Trump even if he wins the GOP nomination. That means that Israel's most prominent elite backers in the GOP would be on the outs in their own party.

This doesn't mean that the GOP is becoming an anti-Israel party. Trump has called himself "pro-Israel" for years. During Israel's 2013 elections, he endorsed Netanyahu for prime minister. Nothing he's said suggests major changes in American policy toward the Israel-Palestine conflict.

Rather, Trump's rise suggests that a Trump-style candidate can lead the GOP to be less hard-line pro-Israel than is typical of the party. Maybe that's because GOP support for Israel was weaker than it looked or, perhaps more likely, that Trump's appeal over the other candidates is simply so powerful that it overcomes his heresy on this issue. But the point is Trump's rise shows that a maximally pro-Israel GOP, even if just in rhetoric, is not necessarily guaranteed anymore.

What this means for the future

Netanyahu's GOP-firewall strategy was meant to solve a problem: Israel's political trajectory seems likely to soften the alliance.

Surveys of US public opinion show that broad American support for Israel rests on the sense of a shared democratic identity between the two countries. But Israel's increasingly indefinite occupation of the Palestinians undermines this perception. This and Israel's increasingly right-wing politics risk alienating more liberal Americans.

This doesn't mean that American liberals, much less America itself, would ever abandon the alliance with Israel, but rather that the alliance would become a little less close, a little more conditional.

And already, important Democratic constituencies — younger voters, black voters, Latino voters — support Israel at lower rates than do other American demographic groups.

Netanyahu's Republican firewall was always risky — openly courting Republicans and spurning Obama appears to have accelerated the process of political polarization on Israel. But Netanyahu appears to have concluded a partisan-tinged alliance was better than a purely bipartisan alliance, because Republicans would be less likely to pressure him over Israel-Palestine issues such as settlements.

But Trump's rise calls this theory into question. Not because Republican voters are about to change their minds on Israel en masse, but because they're clearly willing to embrace GOP candidates who waver on Israel support, if those candidates deliver Trump-style politics.

It's way too soon to predict that the rest of the GOP will come to resemble Trump; the establishment still vehemently opposes him, including over Israel. But he is chipping away, however unintentionally, on the party norm of absolute and unflinching support for Israel. There's no guarantee Trump represents a coming wave of Republican Trumpism, and likewise there is no reason that future Trump-style Republicans will necessarily break with party orthodoxy on Israel.

The point is that Netanyahu has premised his strategy for managing the United States on a bet that the Republican Party's approach to Israel won't change. Trump is making that gamble look a little more dangerous.