Why is Gloucester declared a traitor by Regan?

Gloucester is declared a traitor by Regan because he is loyal to King Lear, who is seen as a rival to Regan and her sister Goneril's ambitions for power. Regan's decision to label him a traitor reflects her ruthless pursuit of authority and her willingness to eliminate anyone who opposes her. Additionally, Gloucester's support for Lear's rightful claim to the throne puts him at odds with Regan's interests, leading her to turn against him. This declaration ultimately results in Gloucester's tragic downfall.