Option 1 -> "the first leg" refers to the first part of a journey or competition, not a speaking ability.
Option 2 -> "the gift of the gab" means having excellent speaking skills, fluency, and persuasiveness.
Option 3 -> "the going rate" refers to the current standard price for something, unrelated to debating skills.
Option 4 -> "the golden rule" refers to treating others as you wish to be treated, not a talent for speaking.
Hence, Option 2: the gift of the gab -> This idiom perfectly describes someone with natural eloquence and persuasive speaking ability, which are essential qualities for winning debates -> correct