Unfortunately, as a lot of area experts have been pointing out, it's almost universal with dictators that they're malignant narcissists. Putin is too, just more intelligent than Trump originally. Their character flaws inevitably lead to their getting more and more isolated and insulated from anyone who could talk sense to them, because they choose sycophants to empower. The circles of access tighten and they ultimately become completely divorced from reality, with the people who would normally provide reality checks simply guessing how best to please them and reinforcing their delusions. Apparently there are a lot of delusions behind this one, some long-standing, not least the obviously insane revanchist obession with restoring the Russian empire's "greatness", but for example, people are saying Putin and leadership legit expected a large amount of Ukrainian military to simply lay down arms in immediate surrender.

So I mean, not only could nobody stop a dictator - as a condition of the kind of power they amass - the type of government they create always exists mainly to feed their egos, which sets them in a spiral to become less and less accountable to reality and also more able to simply deny it.