Which Constitutional principle is Jefferson illustrating in this letter?

Without the specific letter you're referring to, I can provide a general answer. Thomas Jefferson often illustrated the principle of individual rights and limited government in his writings, emphasizing the importance of personal liberty and the protection of citizens' rights from governmental overreach. He believed in the idea that government should serve the people and that its powers should be limited to ensure freedom and justice. If you provide more details about the letter, I can tailor the answer more specifically.