NEW: Hunter Biden is calling the appointment of Merrick Garland as attorney general the "greatest mistake" his father made in office. "My take is this, and rem

NEW: Hunter Biden is calling the appointment of Merrick Garland as attorney general the "greatest mistake" his father made in office. "My take is this, and removing myself from it as much as I can, my personal feelings, is the single greatest mistake of my father's administration was the leadership…