President Joe Biden signed NATO accession protocols for Finland and Sweden, moving the defense alliance closer to adding two wealthy, militarily advanced members amid Russia’s ongoing assault on Ukraine.

Biden’s approval followed overwhelming support from both chambers of Congress earlier this summer, with the Senate ratifying the agreement last week. Efforts to welcome the two Nordic countries to the treaty have received bipartisan support, with Senate Minority Leader Mitch McConnell last week calling their admission a “slam dunk” for national security.

Finland and Sweden have skirted military alliances in the past, but quickly moved to apply for NATO membership in May, a few months after Russian forces invaded Ukraine. NATO ambassadors ratified the accession protocols in July, and member states are currently in the process of doing the same.