I would agree with Kerry that boots on the ground are good.

The West made an error in accepting that Russia has the right to exclusivity of the Ukrainian airspace. If the West recognizes Ukraine as an independent nation, it is up to Ukraine to decide who can fly in their airspace. Ergo, under the reasonable concern that military operations there might endanger neighboring NATO countries and might jeopardize the commercial navigation on the Black Sea, NATO should declare that any Russian planes or rockets a few hundred miles east of NATO borders and a few hundred miles north of the Black Sea shore were legitimate NATO targets. It would mean a great difference for the boots on the ground.

The Western politicians did not dare to do that, for the same reason their predecessors signed the Munich Agreement in 1938.