How does Article 5 apply to Russia’s attack on Ukraine?
Since Ukraine is not a member of NATO, the US is not compelled to protect the country the same way it would if a NATO member nation was attacked.
But many of Ukraine’s neighbors are NATO members, and if a Russian attack extended into one of those countries, Article 5 could trigger direct involvement from the US and other NATO members.
https://www.cnn.com/2022/03/07/politics/what-is-nato-article-5/index.html