No President controls the economy. This is not an economy controlled by the central government. It is a Free Enterprise system. That means the economy is run by private enterprise not public enterprise.
The Constitution does not give the President any duties on fixing the economy.
All the President's duties are prescribed by the Constitution, Lindsay Barker. The President is not required to do anything not provided for in the Constitution. In fact and at law , not supposed to do anything not authorized by the Constitution.
The federal government buys many things, and that affects "the" economy as a whole. However , the _changes_ in government buying and welfare spending are not the driver or determinant of the economy as a whole. The private sector is the main determinant of the economy as a whole. For example, the Wall Street crash of 2007-8 caused the depression we are still suffering from , not actions by the Bush administration. All that war spending by Bush _boosts_ the economy , especially the military-industrial-CIA complex.
Keynes' economic theory is that in recessions , government _deficit_ spending can _help_ get to recovery faster; not that government spending determines the growth of the GDP all the time. Note : it is deficit spending , that is spending that is with more borrowed money and increases the debt,
To reiterate , the Constitution , the only source of Presidential duties and powers , makes no mention of Presidential responsibilities or powers with respect to GDP, unemployment or debt to GDP ratio , etc. Secondly, macro-economics does not hold that increases or decreases in government spending determine the growth of the economy as a whole.