For months, NATO leaders had hoped that when they gathered for their annual summit next week, they could take the opportunity to welcome Sweden as the alliance’s newest member.
Now, that outcome seems all but impossible, as a standoff by Hungary and continued objections from President Recep Tayyip Erdogan of Turkey have dragged the process out, raising questions about when Sweden might join and what success would be needed.
All 31 member states must agree to admit new members, and the split over Sweden risks damaging the alliance’s ability to project a united front against President Vladimir V. Putin of Russia as his forces seek to repel a Ukrainian counteroffensive.
NATO officials say the hope is to get all the alliance’s leaders to agree at the two-day summit beginning Tuesday in Vilnius, the Lithuanian capital, to let Sweden join. Then, the thinking goes, Mr. Erdogan and Prime Minister Viktor Orban of Hungary can push the approval through their respective parliaments.
To this end, Jens Stoltenberg, the secretary general of NATO, will meet senior foreign, defense and intelligence officials from Turkey, Sweden and Finland on Thursday in Brussels, to convince the Turks that Sweden, like Finland, has done enough to win. Turkish objections.
On Tuesday, Foreign Minister Peter Szijjarto of Hungary told reporters that he was in contact with his Turkish counterpart and that if the Turkish position changed, Hungary would not interfere with the process.
That leaves the ball in Mr. Erdogan’s court, and if next week’s summit ends without a deal, it’s unclear what would break the deadlock, or when. NATO officials worry that Swedish membership could then be put on hold for many months, a symbolic win for Mr. Putin and a loss for the alliance.
At the same time, Mr. Stoltenberg argued in an interview that Sweden is already involved in all NATO meetings and in defense planning and military exercises. But Sweden would remain outside NATO’s commitment to collective defense, a core goal of the alliance.
“If there is no agreement in Vilnius, then we have a crisis in NATO, period,” said Marc Pierini, a senior fellow at Carnegie Europe and a former European Union ambassador to Turkey.
On Wednesday in Washington, President Biden met with Prime Minister Ulf Kristersson of Sweden to reiterate American support for Sweden’s membership in the alliance. Mr Biden said he was “anxiously looking forward” to that day, but conceded the decision rested in Mr Erdogan’s hands.
“I want to reiterate that the United States fully, fully, fully supports Sweden’s membership in NATO,” Mr. Biden said. “The bottom line is simple: Sweden will strengthen our alliance.”
In the 14 months since Sweden applied to join the alliance, the subject of its ascension has become caught up in a complex web of issues, including international arms deals and competing concepts of terrorism and freedom of expression.
Turkey has accused Sweden of providing a free operating environment to Turkish dissidents, whom Turkey considers terrorists. These include members of a religious movement that Turkey accused of trying to overthrow Mr. Erdogan in 2016 and supporters of a Kurdish militant organization that has fought a bloody insurgency against the Turkish state.
Sweden has tried to meet Turkish demands by amending its Constitution and toughening its anti-terrorism laws, which only came into effect on June 1. It also agreed to extradite a small number of people wanted by the Turks.
Last month, Sweden’s Supreme Court ruled that Sweden can extradite a Turkish man wanted in Turkey for drug crimes. The man, who has not been identified, told the court he was targeted because he supported a pro-Kurdish political party.
But Swedish courts have blocked at least one other extradition, saying a journalist wanted by Turkey had not committed acts considered crimes in Sweden.
“If you look at Turkey, of course the aim is and has been for over a year to extract as many concessions as possible from Sweden before agreeing to accession,” Mr Pierini said. “If you look at Sweden’s perspective, they are trying to protect their concept of the rule of law.”
Mr. Stoltenberg and other NATO leaders said Sweden had done enough and should be allowed to join the alliance. Many analysts also suspected that Mr Erdogan’s hard line on Sweden was aimed at rallying nationalist voters at home in the run-up to Turkey’s presidential election in May, in which Mr Erdogan won a third term.
But Mr Erdogan’s stance has not changed since the election, and he again attacked Sweden after a protester publicly burned a Koran at a demonstration in the Swedish capital, Stockholm, last week, accusing Sweden of failing to fight Islamophobia. The action appeared aimed at derailing the NATO negotiations and was carried out in front of a large mosque during one of the most important holidays in Islam.
“We have clearly stated that it is our red line to firmly fight terrorist organizations and Islamophobia,” Mr Erdogan said after a meeting with his Cabinet on Monday. “The sooner our counterparts accept this reality, the healthier this process will be.”
The incident frustrated NATO officials, who noted that combating Islamophobia was not among the issues the parties agreed to work on to facilitate Sweden’s accession bid. And the Swedes pointed out that the police tried to ban the protest but were overruled by the courts.
The issue is key for Mr. Erdogan, who has marketed himself to his conservative, religious base at home as a global champion of Islamic causes.
“When it comes to giving the impression to the domestic public that this is a government that actually puts its money where its mouth is, it’s a consistent stance,” said Ahmet Kasim Han, a professor of international relations at Beykoz University in Istanbul. “It fits very well with the public image of the president himself.”
Mr. Han said potential paths to success remain. Sweden could do more to meet Turkey’s demands, he said, or the United States and other NATO members could throw in “sweeteners” such as arms or economic deals to win over the Turks. A thaw in the chilly relationship between Mr. Erdogan and Mr. Biden would also help; the American president did not welcome Mr. Erdogan to the White House, unlike his three predecessors.
“Turkey either wants to have strong sympathies and actions for its own security concerns or wants to make a big deal with Berlin, Brussels and Washington on issues related to larger foreign and security policy agendas,” Mr. Han said.
The Biden administration pushed hard for NATO expansion. Turkey wants to buy $20 billion worth of F-16 fighter jets and other equipment from the United States, but administration officials rejected the idea that Mr. Biden would use this to pressure Mr. Erdogan on NATO expansion.
However, success on Sweden could reduce resistance to the agreement in Congress.
Mr. Biden mentioned Sweden and the arms deal together when he told reporters last month about his call with Mr. Erdogan to congratulate him on his re-election.
“He still wants to work on something about the F-16,” Mr. Biden said of Mr. Erdogan. “I told him we want a deal with Sweden, so let’s do it.”