Few of the levers in a president's hand are attached directly to economic motors. The Chairman of the Federal Reserve Board sets interest rates. Congress makes tax laws. Herds of hysterical investors determine stock prices. Business executives decide to build new factories or move them to Mexico.
Workers make things.
Consumers buy them. The president is inconsequential to all that. The economy is a huge, complex system, with many parts and players. It is wired together in such a way that it goes through ups and downs that are not really in anyone's control. Of course the president can impact the economy.