A major hurdle, however, soon became apparent.
Turkey: No concessions, no accession
Within hours of the Finnish and Swedish ambassadors confirming their nations' intent to join early Wednesday morning, NATO ambassadors considered the request to open accession negotiations. But any expectations of a quick process immediately evaporated.
Multiple diplomatic sources, speaking on condition of anonymity, said while 29 of the ambassadors at the North Atlantic Council (NAC) meeting were ready to agree to open the talks with Helsinki and Stockholm, the Turkish representative said he could not.
Turkish President Recep Tayyip Erdogan had warned he would not agree to admit the two countries without concessionsand he chose to make that stand as soon as the question was formally brought before the allies.
Erdogan says the two countries support terrorism, accusing them of "harboring terrorists" by refusing to extradite members of the Kurdistan Workers' Party, the PKK, and being sympathetic to the Syrian Kurdish militant group, the YPG, also backed by the US.
He is additionally indignant the two countries imposed an arms embargo on Turkey after its ground offensive into northern Syria in 2019.
NATO's tight timeline
The Turkish president knows this moment is particularly vulnerable, due to the urgency the alliance feels to bring the two highly qualified countries under the Article 5 umbrella during wartime. But there's also a more specific timeline: NATO wants the two present at its Madrid summit in late June as "invitees."
While there will still be many months of waiting while each of the 30 allies ratifies the accession, NATO wants to be well into that phase by the summit.
"Erdogan is not in a hurry and everyone else is," one source said, adding that this gives him extra leverage.
That leaves only a very few weeks in which to convince Ankara to acquiesce to opening the accession negotiations.
After that, NATO officials say the discussions with the two governments will be extraordinarily brief — as little as one day each — because they already meet and even exceed the criteria, which include a "functioning democratic political system based on a market economy; fair treatment of minority populations; a commitment to resolve conflicts peacefully; an ability and willingness to make a military contribution to NATO operations; and a commitment to democratic civil-military relations and institutions."
Sources explain that while NAC ambassadors will expect to be kept up-to-date on Turkey's position, it's unknown when the question of the Finnish-Swedish accession negotiations will be put back on the agenda with the expectation of it being approved by the required unanimity. "It's clear this is not something that can be resolved at this level,” one said.
Will Washington weigh in?
But everyone's wondering just where — and in fact, whether — it can be resolved, at least without the involvement of the US.
NATO allies are reluctant to get involved, both to prevent Erdogan from having even more of a platform and to avoid antagonizing him further, possibly cementing his determination to extract the highest price possible. Stoltenberg, who has a good relationship with Erdogan as well as a natural connection with his fellow Nordic leaders, has offered to help mediate.
No such offer yet from US President Joe Biden, who welcomed Finnish President Sauli Niinisto and Swedish Prime Minister Magdalena Andersson Thursday at the White House to underscore American support for their bids, but made no mention of the specific dispute at hand.
Biden said only that the US Congress is ready to quickly consent to Finnish and Swedish accession, "once the perspective of all Allies [is] addressed," after having earlier told reporters: "I am not going to Turkey, but I think we'll be okay."
His Finnish counterpart was more direct. Standing next to Biden, Niinisto assured Ankara that "as NATO Allies, we will commit to Turkey's security, just as Turkey will commit to our security." He added that Finland "condemn(s) terrorism in all its forms, and we are actively engaged in combating it. We are open to discussing all the concerns Turkey may have concerning our membership in an open and constructive manner."
Andersson added that her government is "right now having a dialogue with all NATO member countries, including Turkey, on different levels to sort out any issues at hand."
Those efforts include reminding Ankara of Sweden's record on the PKK, which includes being the first foreign country to declare the group a "terrorist organization" and, now, battling disinformation that Swedish Foreign Minister Ann Linde says is being amplified on social media.
Sticky situation for Stockholm
But Turkey already knows this and it's evidently not sufficient.
Paul Levin, the founding director of Stockholm University's Institute for Turkish Studies, says clearing the obstacles to NATO accession will be tough for Sweden.
"The demands that Ankara has made on Sweden would be very difficult for the Social Democratic government to agree to," Levin told DW, noting domestic concern that Sweden would give up some of its human rights standards in joining the military alliance.
"Frankly, there's not a lot of middle ground. I assume that there will be some Swedish concessions, but it would be hard for them to meet all or even many of the demands."
He recalls that Turkey also threw up roadblocks to NATO plans to enhance Baltic defense ahead of the London leaders' meeting in 2019, using some of the same issues it raised now.
The hitch was eased with a compromise that was never publicly explained.
"I think Sweden really does hope for a US intervention, looking at similar episodes in the past," Levin predicted. All eyes are on deals currently under discussion between Washington and Ankara on US fighter jets.
There is no sign of active intervention yet from the Biden administration, but Levin points to one American attitude that perhaps Erdogan should monitor. Former US Senator Joe Lieberman and Ambassador Mark Wallace suggest in The Wall Street Journal that for "reasons that are political, parochial and irrelevant to the decision, President Recep Tayyip Erdogan has taken a hard line in his efforts to derail the prospective members. This should raise the question of whether Turkey under Mr. Erdogan's leadership belongs in the alliance."
Edited by: Stephanie Burnett