Final answer:
Option D is correct; most government spending functions as an automatic stabilizer, allowing fiscal policy to adjust to economic conditions without needing direct Congressional action, thus reducing the reliance on discretionary fiscal policy.
Step-by-step explanation:
The question addresses the role and limitations of fiscal policy in government budgeting, particularly in the context of mandatory spending on programs like Medicare and Social Security, and the challenges of implementing changes. Option D suggests that most spending acts as an automatic stabilizer, allowing fiscal policy to respond to economic conditions without direct Congressional intervention.
This reflects the fact that in a recession, for instance, there are automatic increases in government spending and reductions in tax revenue due to a higher demand for social services and lower income levels, respectively. Conversely, in a boom, tax revenues increase and spending on social services falls. Because of these built-in stabilizers, the need for discretionary fiscal policy is reduced, making it less vital for Congress to enact frequent fiscal changes in response to economic fluctuations.