In mid-May, Finland and Sweden – two historically non-aligned countries – formally handed in their applications to join the North Atlantic Treaty Organization, or NATO, as the Finnish and Swedish Ambassadors to NATO simultaneously handed in the official letters of application at the military alliance’s headquarters in Brussels. Lauded as an “historical moment” by Secretary General Jens Stoltenberg, he encouraged all 30 NATO allies to expeditiously ratify Swedish and Finnish membership.

Yet, what should be a momentous event in in NATO history is instead met with several obstacles. Russian President Vladimir Putin, citing NATO expansion as one of his justifications for invading Ukraine in February, sent mixed messages about Swedish and Finnish membership in the military alliance. Turkey, a key NATO ally, is reticent in extending membership to NATO’s Nordic neighbors. Despite being NATO’s closest partners already, Sweden and Finland’s hopeful accession into NATO looks like a bumpier ride than ever imagined.

The Neutrality of NATO’s Nordic Neighbors

Ironically, Finland and Sweden did not seriously consider joining NATO until Russia’s invasion of Ukraine. Had Russia never invaded, NATO members would not likely be in discussions about adding its Nordic neighbors into the alliance.

Both countries – though more closely politically and militarily aligned to Western institutions including NATO and the European Union– maintained a degree of military neutrality. Finland, who shares a long border with Russia, stayed neutral for fear of upsetting its eastern neighbor during the Cold War. Similarly, Sweden has enjoyed roughly 200 years of neutrality. It was not until Russia’s invasion of Ukraine earlier this year that most Finns and Swedes began rethinking their membership in NATO.

Putin’s Perplexing Proclamations

Russia’s reaction to the news of Sweden and Finland potentially joining the alliance has been mixed. At first, Mr. Putin admitted that potential membership could have “a negative effect” on relations. He then contradicted his initial reaction by saying that Finnish and Swedish membership in the alliance that he has long railed against was not an immediate threat to Russia.

Attempting to straddle the line between seeming unaffected by its Nordic neighbors NATO membership and angry at the potential of another round of expansion, Mr. Putin elevated the security situation by threatening to use nuclear weapons on its Kaliningrad enclave settled amongst the Baltic states in northeastern Europe, should Sweden and Finland join the 30-member alliance. Russia clearly views another round of NATO expansion as a threat to Russian security, and whether Mr. Putin intends to follow through on his seemingly hollow threats remains to be seen.

Let’s Talk Turkey

Turkey, a key NATO ally, is proving to be another obstacle to expedited membership process. This is becoming increasingly problematic as all 30 NATO allies must agree on Swedish and Finnish membership. Almost immediately, Turkey blocked the fast-tracked accession talks. The reasons uncover a degree of Turkish frustration that runs deep.

For one, Turkish President Recep Tayyip Erdogan objected to Sweden and, to a lesser extent, Finland due to their alleged support of members of the Kurdistan Worker’s Party (PKK), a group which Turkey accuses of separatist tendencies and which the United States and European Union recognize as a terrorist organization. As a result, Turkey is demanding that Sweden extradite more than 30 people who are terrorists in Turkey’s eyes. Turkey also accuses Sweden and Finland of sympathizing with and harboring follower of Fethullah Gulen, a Turkish cleric in exile in the United States whom Mr. Erdogan blames for a failed coup in 2016.

Turkey’s objections to Finnish and Swedish membership in NATO are not limited to the PKK. Turkey is still miffed over restrictions on sales of military equipment imposed by the European Union, including Finland and Sweden, after a Turkish incursion in northern Syria in 2019.

Turkey also desperately wants to return to the U.S.-led F-36 fighter jet program. In 2017, the United States kicked Turkey out of the program after the Turkish purchase of the Russian S-400 defense systems. Most analysts agree that Turkey’s objections have a two-fold purpose. It is possible that Mr. Erdogan is trying to gain concessions from its NATO allies as a means to bring Turkish security concerns to the forefront. Beyond that, analysts also believe that the Turkish government is using this as a leverage to get the United States to agree to Turkey purchasing F-16 fighter jets, something that many Republicans and Democrats in Congress view with growing concern.

The Dangerous Period is Now

As the Washington Post recently noted, Finland and Sweden are most vulnerable to a Russian attack during the period before they join the alliance. Even though both countries have formally applied for membership, this process, even for countries generally expected to be granted admission without much difficulty, can take months or even years. This is becoming increasingly likely due to Turkey stalling the process even more. The danger comes because neither country is yet covered by NATO’s Article 5 mutual security clause, which states that an attack on one is an attack on all.

Several allies have offered assurances that both Nordic countries can expect protection in the interim period. The United Kingdom even went so far as to sign security pacts with Sweden and Finland to assure their protection in the event of an attack. In May, British Prime Minister Boris Johnson, though plagued by his own domestic political troubles, traveled to both Stockholm and Oslo to sign a bilateral security deal offering each country security guarantees should Russia attack.

France, another key NATO ally, announced it would defend the hopeful Nordic members in the event of an attack. Three other NATO allies – Iceland, Norway, and Denmark – released a joint statement, confirming they would be willing to protect Sweden and Finland for their decision to join NATO. The likelihood of Russia attacking either country remains remote, especially because the Russian military remains bogged down in its war in Ukraine.

Overall, ensuring that Sweden and Finland have a degree of security commitments from NATO allies during the transition period remains critical.

Rhetoric is Not Enough

Like its NATO allies, the United States stands firmly behind Sweden and Finland’s applications to join the alliance. Shortly after submitting their formal applications, Sweden’s prime minster Magdalena Andersson and Finland’s president Sauli Niinistö visited the White House.

Flanked by the leaders of the Nordic countries, Mr. Biden vowed to “confront” any threats to the security of both countries while they are waiting during the application process. “Today,” he began, “the president, the prime minister and I committed that we’re going to work together to remain vigilant against the threats to our shared security and deter and confront any aggression while Finland and Sweden are in this accession process.”

Rhetoric is not enough. Mr. Biden’s White House statement, which fails to solidify such support, should go one step further. As NATO’s most powerful member, the United States should go a step further in assuring Sweden and Finland that the United States, as well as all NATO allies, have their backs in the event of any attack, whether from Russia or not. The Biden administration should follow the lead of the United Kingdom, which signed mutual security pacts with the Nordic countries.

Sweden and Finland, no doubt, can rest assured that most NATO members – despite Turkey’s recent balking – would have their backs immediately even if not yet covered by NATO’s Article 5. Mr. Biden, too, should also make clear that should either Finland or Sweden be attacked during the interim period for which they are awaiting official admittance to NATO, the United States will come to their defense just as they would any NATO or other treaty ally.