The Founders of the American Constitution created a robust executive branch of government and limited its ability to become a tyranny, not principally using checks, but by the creation of balances. If citizens viewing the power of the executive branch in the 21st century do not perceive any definite limits, it is because the body politic has failed to maintain its vigilant knowledge and understanding of the important limiting design of the checks and balances in the Constitution.
The balance of powers, and the limitation on the executive branch, may be well understood by simply observing how this legendary balance is intended to form domains and create boundaries that are drawn closely around the executive power. The Founders intended the executive branch of government to have the robust power to protect the body politic and the citizens. The dangers in the world often appear in the immediacy of the moment -- almost as a surprise. But just as readily, the executive branch in the immediacy of the moment must exercise its powers to protect the body politic and the citizenry.
What the Constitution denies the executive branch is the power to look ahead far into the future and create new laws. The executive branch, of course, must anticipate dangers to the body politic. But it is expressly confined to enforcing existing laws and it is forbidden to create new laws.
This robust executive power -- to exercise coercive force to protect the body politic -- terminates when the danger has been contained, and jurisdiction is passed to the judicial domain. The judiciary looks back to determine and review the facts of the matter, which crucially now are in the past; and, the judiciary must look back more deeply to research and chronicle the legislative intent in order to determine whether and how the laws should apply.