With the end of the Cold War, the Baltics managed a miracle journey from captive nations to members of NATO, joining every international organization they could and putting their trust in Western norms and credibility. They have all become vibrant, multiparty democracies.
They are small, yes, and far away, yes. But the line has to be drawn somewhere. If not at Tallinn, how about Helsinki? If not in Vilnius, in Warsaw? If in none of those places, in Prague or Berlin? Russia must have a westernmost boundary, enforced by a defensive alliance of like-minded Western democracies; otherwise Putin will be tempted to act yet again on his open musings about creating a greater Russia.
And if the U.S. simply turns its back on its signed-and-sealed Article 5 commitment to mutual self-defense under the NATO treaty, what is to become of the credibility of its alliances and assurances for everyone else? If the Baltics ever fall, it will be very bad news for Taiwan and the effort to check Chinese expansionism.