Supporting the idea, while suggesting he can't provide proof, Marco Rubio (Vice President of Senate Select Committee on Intelligence) has this to say: "I wish I could share more,but for now I can say it’s pretty obvious to many that something is off with #Putin

He has always been a killer,but his problem now is different & significant

It would be a mistake to assume this Putin would react the same way he would have 5 years ago" Source: https://twitter.com/marcorubio/status/1497393912821915648

Later, Rubio says: "Let me stress again that we are NOT dealing with 2008 #Putin

It is a grave error to assume he will make the same calculations & decisions today that he would have made in the past

The old Putin was a cold blooded but calculating killer

This new Putin is even more dangerous" https://twitter.com/marcorubio/status/1497968757091807234

Obviously, he's not going so far as to say that Putin has "lost his marbles" and Rubio definitely has his own agenda. My impression is that either Putin's cognitive state has changed over the last five years or Russia's doctrine of "escalate to de-escalate" has changed the playbook.