The U.S. and key NATO members should occupy western Ukraine and establish a no-combat zone. They should take action despite Putin’s nuclear threats, and they should act immediately, because the window of opportunity is closing.
A full NATO occupation of western Ukraine would preserve a free and independent nation in the west, while diminishing chances of Ukrainian success in the east. Yet those chances seem low at present, despite President Zelenskyy's incredible leadership.
In order not to provoke Vladimir Putin into direct conflict with NATO/U.S. forces, it would have to be a two-sided no-combat zone, off limits to both Ukrainian and Russian aircraft and ground troops and the transit of arms supplies to Ukrainians fighting in the east. It could not be a protected zone from which Ukrainian troops and planes could launch attacks on Russian forces to the east.
Suspension of arms support for Ukrainian fighters in the east would be a bitter pill for President Zelenskyy. Yet in the absence of any NATO action, the crisis is likely to end in total defeat for Ukraine (and the U.S., NATO and the West).
The east-for-the-west dynamic might offer a welcome off-ramp to Putin who has bitten off a lot, if not too much, to chew.