Israel’s relationship with Russia is in some ways its most important and also its most dangerous. While the U.S.-Israel relationship is the only one that is vital to guaranteeing Israel’s fundamental security, the relationship with Russia has a larger impact on the daily threats that Israel faces given the Russian role in the Syrian civil war. Prime Minister Netanyahu has ably managed ties with Moscow, with his trip to Russia to meet with President Putin two weeks ago the fifth in the past year, but the reality is that despite Israel’s best efforts, tension with Russia is bound to escalate. Israel and Russia’s redlines with regard to the outcome in Syria are in fundamental conflict, and papering over the differences is becoming increasingly harder to do.

Russia-Israel ties under Netanyahu and Putin have reached a historical apex for the two countries, partly because of the rapport between the two men and partly because of larger structural factors. From Israel’s perspective, closer ties with Russia make for good domestic politics. Over 10% of Israel’s population hails from the former Soviet Union, and Russian Jews maintain cultural and economic links to their former homeland. Soviet Jews have risen to the top of the government, with Israeli Defense Minister Avigdor Lieberman and Knesset Speaker Yuli Edelstein the most recent examples. Russia is also seen as a strong ally in Israel’s battle against terrorism as Russia has its own homegrown terrorist threat, and the Kremlin has also historically been inclined not to harshly criticize Israeli settlement policies despite its support of a Palestinian state.

But it is due to defense concerns on both sides that the relationship has deepened and become more important. One of the few advantages that Georgia had in its five-day war with Russia in 2008 over South Ossetia was its Israeli drones, which were far superior to the domestically-produced models flown by Russia and a fact that did not escape Moscow’s attention. It led Russia to subsequently make four purchases of Israeli drones, a seemingly ordinary transaction made remarkable by the fact that it was the first time Russia had ever bought arms from a foreign country. As Russia has increased its military activity in Syria and its near-abroad, its desire for Israeli military technology has only grown, and thus its relationship with Israel has become more important.

On the Israeli side, Russia’s involvement in Syria directly impacts Israel and makes closer relations a necessity. For the Israeli government, Russia’s heavy presence in Syria has been a blessing and a curse. The blessing is that Israel has been able to repeatedly strike Iranian arms convoys destined for Hizballah without Russian interference despite flying hundreds of sorties through Russian-controlled territory, since Jerusalem and Moscow have worked out a deal preserving Israel’s ability to strike these targets and have coordinated to a near-perfect level. Were Israel trying to operate in Iranian-controlled territory rather than Russian, things would be far messier. The fact that Russia purposely turns a blind eye to Israeli strikes on these weapons shipments – despite the extraordinary fact that Israel is oftentimes blowing up weapons that Russia itself has supplied to Iran – also limits the fallout, as it makes it difficult for Iran to retaliate against Israel in response. The curse, however, is that in having to rely on Russia’s good graces, the Israeli military is operating at the mercy of a larger power and must also limit itself to the parameters of what it has agreed upon with Moscow, rather than being able to target Iranian fighters in Syria to whatever larger extent it wishes. Russia’s ownership of the Syrian civil war provides Israel with a greater degree of freedom but also a greater degree of restriction.

While the relationship has remained on track up until now, it has been destined to unravel from the day that Russia entered Syria, and indeed the first loose threads are now beginning to show. No matter how good the coordination mechanism between the two sides, the fundamental conflict at the heart of Israeli-Russian views on Syria is that Israel’s redline is the establishment of a permanent Iranian presence in Syria and Russia’s redline is the elimination of a permanent Iranian presence in Syria. At the outset of the Syrian civil war, Israeli government and military opinion was split as to whether it would be better for Bashar al-Assad to remain in power or better for him to be toppled. That debate has decisively shifted toward the latter as Assad has solidified his rule over western Syria with a serious assist from Iran, leading not only to a more robust Hizballah presence in Syria but Islamic Revolutionary Guard Corps soldiers as well. As the Israeli defense and intelligence establishment came to a near-consensus on the dangers of Assad’s continued tenure given his ever larger reliance on Iran and his further cementing as an Iranian proxy, Russia made it clear that it will not abandon Assad and that its own core interest in Syria is keeping him – and the Iranian influence that is bound up with him as a necessary byproduct – right where he is. Israel cannot abide Assad staying and Russia cannot abide him going.

This situation was manageable so long as Israel was content to confine its actions in Syria to striking Hizballah and breaking up any efforts to supply it with advanced game-changing weaponry, such as S-300 anti-aircraft missiles. But with intelligence that Iran is now beginning to establish permanent bases in Syria, the Israeli calculus has understandably changed. Russia’s, however, has not. It was notable that in the aftermath of the Netanyahu-Putin summit two weeks ago where Netanyahu raised his concerns about preventing an Iranian military presence on Israel’s northern border, neither side indicated that it was particularly satisfied with the outcome of the discussion. Furthermore, one week later the Israeli ambassador to Russia was summoned to explain an Israeli strike that hit close to a Russian military position, introducing a new level of tension into the relationship, and Israel had to bat down the Assad government’s claim that Russia had informed Israel that it could no longer fly missions in Russian-controlled Syrian airspace.

It is an enormous accomplishment of Netanyahu’s diplomacy that the situation with Russia has proceeded so smoothly until now, particularly when juxtaposed against the backdrop of downed planes and economic sanctions that have marked the Russia-Turkey relationship over Syria. But Israel is now entering an untenable situation, in which it will have to choose between risking open conflict with Russia – something that both sides will be desperate to avoid – or sitting on its hands as Iran digs in across from IDF positions on the Golan and plants missile batteries on Syrian territory for the purposes of targeting Israeli cities and towns. Israel was right to worry about Iranian ambitions in the region, but it is the Russian relationship with Iran over Syria rather than the American relationship with Iran over the nuclear deal that will prove to be the thornier dilemma to navigate.