Final answer:
The likely impact on the economy of enacting expansionary fiscal policy without changing tax rates is an increase in government spending, which can stimulate economic growth.
Step-by-step explanation:
If Congress enacts expansionary fiscal policy but does not change tax rates, the likely impact on the economy is an increase in government spending. This can lead to an increase in aggregate demand and stimulate economic growth. With increased government spending, businesses may experience higher sales, leading to increased production and job opportunities. However, without tax rate changes, the impact on individual households may vary depending on their income levels and spending habits.