WASHINGTON (NYTIMES) - When President Recep Tayyip Erdogan of Turkey threatened this month to block Nato membership for Finland and Sweden, Western officials were exasperated - but not shocked.

Within an alliance that operates by consensus, the Turkish strongman has come to be seen as something of a stickup artist.

In 2009, he blocked the appointment of a new Nato chief from Denmark, complaining that the country was too tolerant of cartoons of the Prophet Muhammad and too sympathetic to "Kurdish terrorists" based in Turkey.

It took hours of cajoling by Western leaders, and a face-to-face promise from then-President Barack Obama that Nato would appoint a Turk to a leadership position, to satisfy Mr Erdogan.

After a rupture in relations between Turkey and Israel the next year, Mr Erdogan prevented the alliance from working with the Jewish state for six years. A few years later, Mr Erdogan delayed for months a Nato plan to fortify Eastern European countries against Russia, again citing Kurdish militants and demanding that the alliance declare ones operating in Syria to be terrorists.

In 2020, Mr Erdogan sent a gas-exploration ship backed by fighter jets close to Greek waters, causing France to send ships in support of Greece, also a Nato member.

Now the Turkish leader is back in the role of obstructionist, and is once again invoking the Kurds, as he charges that Sweden and Finland sympathise with the Kurdish militants he has made his main enemy.

"These countries have almost become guesthouses for terrorist organisations," he said this month. "It is not possible for us to be in favour."

Mr Erdogan's stance is a reminder of a long-festering problem for Nato, which currently has 30 members. Russia's invasion of Ukraine may have given the alliance a new sense of mission, but Nato must still contend with an authoritarian leader willing to use his leverage to gain political points at home by blocking consensus - at least for a time.

It is a situation that plays to the advantage of President Vladimir Putin of Russia, who has grown friendlier with Mr Erdogan in recent years. For the Russian leader, the rejection of Swedish and Finnish admission into Nato would be a significant victory.

The quandary would be simpler were it not for Turkey's importance to the alliance. The country joined Nato in 1952 after aligning with the West against the Soviet Union; Turkey gives the alliance a crucial strategic position at the intersection of Europe and Asia, astride both the Middle East and the Black Sea.

It hosts a major US air base where US nuclear weapons are stored, and Mr Erdogan has blocked Russian warships headed toward Ukraine.

But under Mr Erdogan, Turkey has increasingly become a problem to be managed. As prime minister and then as president, he has tilted his country away from Europe while practicing an authoritarian and populist brand of Islamist politics, especially since a failed coup attempt in 2016.

He has purchased an advanced missile system from Russia that Nato officials call a threat to their integrated defence systems, and in 2019 he mounted a military incursion to battle Kurds in northern Syria who were aiding the fight against the Islamic State of Iraq and Syria (ISIS) group with US support.

"In my four years there, it was quite often 27 against one," said Mr Ivo Daalder, a US ambassador to Nato during the Obama administration, when the alliance had 28 members.

Mr Erdogan's objections to the membership of Sweden and Finland have even renewed questions about whether Nato might be better off without Turkey.

An opinion essay this month that was co-written by Mr Joe Lieberman, a former independent US senator from Connecticut, argued that Mr Erdogan's Turkey would flunk the alliance's standards for democratic governance in prospective new member states.

The essay, published by The Wall Street Journal, warned that Ankara's policies, including a coziness with Mr Putin, had undermined Nato's interests and that the alliance should explore ways of ejecting Turkey.

"Turkey is a member of Nato, but under Mr Erdogan it no longer subscribes to the values that underpin this great alliance," wrote Mr Lieberman and Mr Mark Wallace, CEO of the Turkish Democracy Project, a group critical of Mr Erdogan.

Some members of Congress have said as much. "Turkey under Erdogan should not and cannot be seen as an ally," Senator Bob Menendez, the top Democrat on the Senate Foreign Relations Committee, said after Turkey's 2019 incursion into Syria.

But Nato is a military alliance, and Turkey, with the second-largest army in the organisation, an advanced defence industry and its crucial geographic position, plays a vital role.

Western officials say that Turkey would only cause more problems as a resentful Nato outsider - and one that could align itself more closely with Russia.

"Turkey has undermined its own image," said Mr Alper Coskun, a former Turkish diplomat who is now a senior fellow at the Carnegie Endowment for International Peace. But, he added, "it is still a critical member of the alliance."

Once again, the question is what will mollify Mr Erdogan and ensure his support for admitting Sweden and Finland.

President Joe Biden underscored US support for the move when he hosted the two nations' leaders at the White House this month and praised a larger Nato as a check against Russian power.

"Biden took an extremely exposed, high-visibility position by inviting them to Washington," said Mr James Jeffrey, a US ambassador to Turkey during the Obama administration.

Most analysts believe that Mr Erdogan will not ultimately block the accession of Sweden and Finland, but that he wants to highlight Turkey's own security concerns and make domestic political gains before elections in his country next year.

Mr Biden administration officials downplay the standoff and expect Mr Erdogan to reach a compromise with Finland and Sweden. Turkish officials met in Ankara with Finnish and Swedish counterparts for several hours last week.

Ms Julianne Smith, the US ambassador to Nato, said that "this appears to be an issue that they have with Sweden and Finland, so we'll leave it in their hands." She added that the US would provide assistance if needed.

Appearing with Finland's foreign minister in Washington on Friday (May 27), Secretary of State Antony Blinken said he was "confident that we will work through this process swiftly, and that things will move forward with both countries."

Mr Emre Peker, a London-based director for Europe at the Eurasia Group, a private consulting firm, said that he did not believe that Mr Erdogan was seeking concessions from Washington.

He expressed confidence that Turkey could work out an agreement with Sweden and Finland with the mediation of the Nato secretary-general Jens Stoltenberg.

Mr Erdogan's main priorities are getting his country's security concerns about Kurdish separatists heard and getting the arms embargoes lifted, Mr Peker said.

Some US analysts are sceptical. Mr Eric Edelman, a former US ambassador to Turkey and Finland, warned that Mr Erdogan could be seeking to curry favour with Mr Putin - or at least ease the anger in Moscow over the sale of lethal drones to Ukraine's military by a private Turkish company.

"He has this very complicated relationship with Putin that he has to maintain," Mr Edelman said. "This is a good way of throwing a little bone to Putin - 'I'm still useful to you.'"

Others believe the Turkish leader wants a payoff from Washington. Mr Erdogan is angry that the US denied Turkey access to the F-35 stealth fighter after his 2017 purchase of the Russian S-400 missile system.

Turkey is now lobbying instead to buy enhanced F-16 fighters but has met stiff resistance in Congress from the likes of Mr Menendez.

Mr Erdogan may also be seeking presidential attention. He had a friendly rapport with former President Donald Trump, but Mr Biden has kept his distance.

"This is a man who needs to be at centre stage," said Mr Daalder. "This is a way to say: 'Hey, I'm still here. You need to pay attention to my issues.'"