I believe an attempt was made to poison Putin before the invasion. It may have been factored into his logic to order it. Just like nations might start wars to mask internal economic problems, people (like Putin) can start fights to mask problems they don't want to deal with.

Putin's problem, and those around him, is that he's old with no succession plan that makes everyone in his clique feel safe.

They're all old men who confuse the effects of Viagra with real virility.