Political parties in America don't have a traditional, singular "party leader" per se. The President, House Speaker (or Leader if the party does not hold speakership), and Senate Leader generally consider policies within their purview and consult with each other as necessary. A national committee governs a party outside of government.

Trump has an outsized presence and influence upon the Republican Party, both as President and as an ordinary American citizen, but this is rather unusual and not the norm.