What is the primary source of uncertainty over the limits on presidential power?

Some presidents win their elections by greater margins than others.
Constitutional amendments have greatly increased presidential powers.
The constitutional definition of executive powers is broad and unspecific.
Some presidents increase power in times of need.

Question

What is the primary source of uncertainty over the limits on presidential power? 

Some presidents win their elections by greater margins than others.
Constitutional amendments have greatly increased presidential powers.
The constitutional definition of executive powers is broad and unspecific.
Some presidents increase power in times of need.

3ssence · Answer

B, constitutional amendments have greatly increased presidential powers