Finland is poised to formally apply for NATO membership as early as May, according to top officials. Finnish prime minister Sanna Marin stated on Friday that the country plans to vote on sending an application to join the alliance by midsummer. “I think we will have very careful discussions, but we are also not taking any more time than we have to in this process, because the situation is, of course, very severe,” said Marin during a press conference. "I think we will end the discussion before midsummer."

Former Prime Minister Alexander Stubb said the government will likely vote on the issue before the end of May, in time for the NATO’s June summit in Madrid. "The Finns think that if Putin can slaughter his sisters, brothers, and cousins in Ukraine, as he is doing now, then there is nothing stopping him from doing it in Finland. We simply don't want to be left alone again," Stubbs said, according to Agence France-Presse.

Finland could soon be followed by Sweden, which is reportedly laying NATO accession plans of its own. "When Russia invaded Ukraine, Sweden's security position changed fundamentally," the country’s ruling Social Democratic Party said in a statement on Monday.

Though both countries have a long history of collaborating with NATO in joint exercises and interoperability initiatives, Finland and Sweden have historically abstained from joining military alliances. This apparent policy shift can partially be attributed to changes in popular perception since Russia’s invasion of Ukraine on February 24. "If you look at public opinion in Finland and Sweden, and how their views have changed dramatically over the past six weeks, I think it's another example of how this has been a strategic failure," a senior State Department official told CNN.

Washington appears to support NATO expansion into Sweden and Finland, and it was reportedly in contact with both countries over their possible accession during high-level talks earlier in April. NATO chief Jens Stoltenberg previously said Sweden and Finland “can easily join this alliance if they decide to apply,” pointing to their high degree of interoperability and compliance with NATO standards.

Moscow has warned Sweden and Finland against joining the alliance, threatening that such moves will provoke a Russian military response. “It is obvious that [if] Finland and Sweden join NATO, which is a military organization to begin with, there will be serious military and political consequences,” Sergei Belyayev, head of the Russian Foreign Ministry’s European department, told Russian reporters.“[It] would require changing the whole palette of relations with these countries and require retaliatory measures,” he said.

Kremlin spokesman Dmitry Peskov said Russia does not view the potential NATO accession of Finland and Sweden as an existential threat, but that such an outcome will nonetheless warrant countermeasures on the part of Moscow. "We'll have to make our western flank more sophisticated in terms of ensuring our security," he said, without elaborating on a specific policy response.

Mark Episkopos is a national security reporter for the National Interest.

Image: Reuters