If you're looking for synonyms for the phrase "cracks the whip," there are several alternative expressions you can use. For instance, you might say someone "wields authority," "holds the reins," or "calls the shots." Other options include "leads the charge," "takes the helm," or "sets the tone." These phrases all convey the idea of someone being in charge or taking charge of a situation, whether that means asserting their authority or simply setting the direction for others to follow. Whatever wording you choose, the key is to convey a sense of decisiveness and control, suggesting that the person in question is not to be trifled with.