IS CONTINUOUS LYING BY THE PRESIDENT OF A COUNTRY TREASONABLE?

“The buck stops here,” said Harry Truman.
When the president of a country is a mythomaniac, can any citizen be prosecuted for perjury?

Does executive privilege include executive lying?
If the president of a country cannot be trusted, can any citizen be trusted?

The macabre and disgraceful use of puerile and pathological memes by the president of any country is enough grounds for impeachment.
If this describes the behavior of any president that you know, you can add the name.