The legislative power severely limits the authority of the executive. There is a large imbalance between the demands and expectations on the President and his position to respond to them. The president cannot get his policies adopted by Congress without long delays and a lot of bargaining.Some rights of the executive branch has allowed the president overcome some limitations in performing roles such as commander in chief, chief diplomat, and chief legislator.
(Example)- When the president declares war as Commander and Chief, the congress has to agree with the deploitation, through checks and balances. Even though that's the case, in the Vietnam war, the president has acted without congressional approval.