War in Ukraine and the threat of conflict in the Baltics raise fundamental questions about the West’s military alliance. What is NATO for? And is it up to the job? More countries have been joining the club, but those who foot the bill seem to be becoming less keen to do so. Do would-be aggressors still believe that an attack on one NATO member would be treated as an attack on all? Our witnesses include a former senior commander and the man who, until a few months ago, led the alliance.

(Photo: Romanian army soldiers from the guard regiment hold NATO membership countries' flags at NATO flag raising ceremony in Bucharest, 2004. Credit: Daniel Mihailescu/AFP/Getty Images)