Final answer:
The President formally enacts an economic stimulus bill by signing a bill that Congress has passed. This is a key aspect of the President's constitutional role in the legislative process, along with the power to veto or pocket veto legislation.
Step-by-step explanation:
The president would use their formal power to sign a bill which Congress has passed in order to enact an economic stimulus bill. This is the constitutional authority the President wields in the legislative process. While presidents cannot introduce a bill in Congress directly, they can use their influence through various means to persuade Congress and public opinion regarding desired legislation. If the president signs the bill, it becomes law unless the bill states otherwise. Aside from the power to sign legislation, the president may also veto a bill, return it to Congress with a veto message, or utilize a pocket veto if Congress adjourns within ten days of sending the bill to the President.