Lester, everyone backs down when defeated. That is the definition of "defeated."

The issue that Dunn makes clear is that the rest of the world, and particularly the US, doesn't care enough about who controls Crimea, the Donbass, and possibly all of Ukraine enough to want to defeat Russia.

Paraphrasing Obama in 2016, there is no compelling argument for the US (or the EU) to fight Russia over Ukraine.

One most common argument made is that Russia will roll on to the EU if it is not stopped in Ukraine, just like Nazi Germany with the Sudetenland and then Austria. There is little evidence to support that theory, and far more counterveiling evidence, that Russia's actual goals are the ones they stated at the start of their invasion.