He is suggesting that a no-fly zone should have been instituted prior to the invasion, at the invitation of Ukraine. This would have produced significantly different military and diplomatic implications; it would have required Russia to be the aggressor, and attempt to strike NATO aircraft preemptively before mounting their initial attacks in Ukraine.

If implemented now, a no-fly zone would require NATO aircraft to behave offensively, and would require strikes on Russian air defenses on the ground as well as aircraft.