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.

Answer 1

"The constitutional definition of executive powers is broad and unspecific" would be the best option, since things like executive orders can be made at any time and can go against the wishes of Congress.