They have some influence. The fed chief is nominated by them. Laws they support get priority. Their policies can have effects on consumer confidence and economic activity, I mean americans belive the president is powerful so true or not their economic behavior is affected, and that isn't just consumers but investors as well. Let's say biden threatened nuke war against russia, that will crash stocks or mention tariffs on China which will affect some stocks more than others. CEOs also use what they say as an excuse to do things.