Final answer:
The most impactful expansion of presidential power is taking decisive action in wartime.
Step-by-step explanation:
The expansion of presidential power that I think is most impactful is taking decisive action in wartime.
Firstly, during times of war, the president becomes the Commander-in-Chief of the military, which grants them significant authority to make quick and critical decisions. This includes deploying troops, conducting military operations, and making strategic decisions to protect the nation.
Secondly, the president's wartime powers often extend beyond military actions. They can also take executive actions to maintain national security, such as implementing surveillance programs or enacting travel restrictions. These measures can have a profound impact on the rights and freedoms of individuals, making the president's role in wartime a highly consequential expansion of power.