But, however complicated NATO membership looks for Sweden politically, it would be dangerous to be left outside the alliance if Finland joins, since the two countries are each other’s closest defense partners and plan for war together, Ms. Wieslander, a Swede who is the Atlantic Council’s director for Northern Europe, said in an interview.
“We always consider Finnish security together with our own,” she said.
Opinion is shifting quickly in Sweden, too, with about 50 percent of people now in favor of joining NATO, rising to 62 percent if Finland joins, Ms. Wieslander said. In Finland, a recent poll had 68 percent in favor joining the alliance, rising to 77 percent if the president and government recommend it.
In Sweden, an all-party parliamentary group, led by Foreign Minister Ann Linde, is studying the issue with a report due May 31. That deadline may be accelerated, because a decision to join NATO would have to pass Parliament with a solid majority, and that would depend on the Social Democrats shifting their position, Ms. Wieslander said.
In the last election of 2018, the Social Democrats’ vote share fell to 28.3 percent, their lowest since 1908, so they are more sensitive to public opinion now than before, and just this week, the party announced that it was reconsidering its position on NATO.