Without question, Russia is committing horrific, inexcusable aggression against Ukraine, and imperialist attitudes in Moscow run deep. But partly because of those attitudes, Russia’s leaders are also reacting to NATO’s expansion. Folding Ukraine into the alliance won’t end that impulse, even with U.S. backing and the nuclear guarantee it brings. Ukraine’s best path to peace is to be well armed and supported outside NATO. (…)

In the run-up to NATO’s summit in 2008, Mr. Bush wanted to give Ukraine and Georgia a formal path to enter the alliance, called a Membership Action Plan. Before the meeting, William Burns, the current C.I.A. director who was then ambassador to Russia, cautioned that such a move would have deadly consequences.