the.com/whip hand

means The position of control or advantage in a situation — the upper hand that lets you dictate what happens next.

from Literal before it was figurative: in driving a horse-drawn carriage, the 'whip hand' was the hand (usually the right) that held the whip, while the other managed the reins. Whoever controlled the whip hand controlled the pace and direction of the horses. By the 1600s–1700s the phrase had galloped into general English, meaning anyone holding decisive control or advantage over another — the horse long gone, the grip of mastery remaining.