Istanbul is a city best viewed from the sea. For hundreds of years, sailors have watched its spires and domes come into view on the horizon as they pass through the Bosporous, one of the world’s busiest waterways. As empires throughout history have found out, whoever holds the keys to this megapolis controls the container ship-spotted straits that link the Mediterranean to the south coast of Russia and Ukraine.

That’s why when Turkey joined NATO in 1952, it was seen as a major Cold War victory, leaving access to the ports of the Soviet Union at the discretion of the US-led bloc. In the decades that followed, however, the country has become the Alliance’s most awkward member, criticised for its close ties to Moscow and deep rifts with the West.

In recent months, Ankara has refused to join its partners in imposing sanctions on Russia, despite its own long-standing interests in Ukraine, instead preferring to transfer advanced attack drones to Kyiv and pile on pressure for a diplomatic solution to the war. Yet at the same time, it has closed the Bosporous to warships, effectively preventing Vladimir Putin’s navy from sending reinforcements to the region.

Turkey has also wasted no time in rushing to fill the space left by Russia’s ongoing economic collapse, ushering in vast amounts of cash from oligarchs and officials desperate to get their assets out of the country. Meanwhile, it has used the fact that Putin’s top brass are distracted to further strengthen its own hold over the Caucasus, backing long-standing ally Azerbaijan in a series of increasingly fractious clashes with Moscow’s ally, Armenia.

Now though, threatening to block the accession of Finland and Sweden to NATO, which requires the support of all 30 existing members, President Recep Tayyip Erdoğan is being accused of doing the Kremlin’s bidding. However, the strongman leader has made it clear his opposition isn’t unconditional, and there is a deal to be done.

“Unless Sweden and Finland clearly show that they will stand in solidarity with Turkey on fundamental issues, especially in the fight against terrorism, we will not approach these countries’ NATO membership positively,” Erdoğan told the head of the Alliance, Jens Stoltenberg, over the weekend.

The row boils down, at least in part, to claims that the two Scandinavian nations, which have large Turkish communities, play host to “militants” and activists from Kurdish independence groups like the PKK, which are outlawed and actively prosecuted by Ankara. In addition, Erdoğan claims Stockholm and Helsinki have harboured supporters of cleric Fethullah Gulen, the US-based preacher he insists was behind a failed 2016 coup. Western governments have been skeptical of the case to crack down on both and, more often than not, refused to extradite those Turkey claims are dangerous terrorists and criminals.

While that particular standoff is unlikely to be up for debate as part of any talks over NATO’s two prospective new members, it offers Erdoğan a convenient pretext to put other issues on the table.

Chief among them is expected to be Turkey’s exclusion from a number of procurement programmes that offer allies a chance to get their hands on high-tech American hardware. While the two are, at least on paper, close allies, Washington went as far as to sanction Ankara in response to its decision to buy Russian-made S-400 anti-aircraft missile systems, by barring it from acquiring both its own Patriot rockets and advanced F-35 fighter jets.

In recent weeks, with Moscow looking like an increasingly unreliable partner for arms exports, given restrictions on military components have ground many of its factories to a halt, Ankara has refreshed its demands to be allowed to buy US tech. “What the West must do is deliver the F-35 fighter jets and Patriot batteries to Turkey without preconditions,” Fahrettin Altun, a top Erdoğan aide, wrote in an op-ed for The Wall Street Journal in March.

The effective embargo has even been raised explicitly in talks about Sweden and Finland joining NATO, with Ibrahim Kalin, another presidential adviser, reporting that the two countries’ diplomats had a “positive attitude” to demands that arms exports be reinstated when they met earlier this week. Whether Washington is as willing to drop its objections and share hardware with a country it isn’t certain it can trust remains to be seen.

By holding up the process, many in the West will claim Erdoğan is dancing to Russia’s tune. In reality, Turkey isn’t content with blindly backing either camp – as a nation with its sights set on being the dominant power from the Mediterranean to Central Asia, it is playing its own game. And it may well win this round.