Dotard is a NYC conman who has long and deep associations with the Mafia Don organized crime. It’s impossible not to, in NYC real estate.

SO, when he uses the term ‘rat’ as when he discusses his lawyer, Michael Cohen, he knows of what he speaks.
A rat is lower level criminal who ‘flips’ on his upper level mob bosses.
It’s a common term with a meaning known to nearly everyone.
SO, it’s the perfect term for Dotard to use for his ‘criminal’ lawyer.
A rat, who’s singing, giving details to prosecutors.
Who doesn’t understand that?
Even the sheep who don’t CARE about the Liar in Chief being a criminal gotta understand.....