The Reagan to Bush Sr. "letter" is fake. It was a joke, a parody.
Reagan did indeed leave Bush a note – not a letter (that started with Bush Sr. to Clinton), but a note. It was short, warm and friendly. Ended with Reagan saying he would miss their Thursday lunches and with kind words for Barbara.
Look it up.
https://www .forbes.com/sites/billwhalen/2017/09/03/on-a-sad-note-even-notes-between-presidents-arent-what-they-used-to-be/#103f16a92878
The weed thing gives Trump bargaining chip to force those smoking blue states to suppprt his immigration plans. They need the marijuana money, and the feds threaten that.
It’s all about the $$. Smart play.