The U.S. Constitution is built from the ground up to prevent a dictatorship. It was a topic into which the founders invested substantial thought.
The Constitution is carefully designed to frustrate the aspirations of tyrants through two principal mechanism: checks and balances and popular elections.
Checks and Balances
The first line of defense is in the design of three coequal branches of government in which the power of each branch of government is checked by the other two. As Madison wrote in Federalist 51:
“If men were angels, no government would be necessary. If angels were to govern men, neither external nor internal controls on government would be necessary. In framing a government which is to be administered by men over men, the great difficulty lies in this: you must first enable the government to control the governed; and in the next place oblige it to control itself. A dependence on the people is, no doubt, the primary control on the government; but experience has taught mankind the necessity of auxiliary precautions.”
In this careful balance of power, each branch, and ultimately the people, will regulate against a despot. As Madison wrote, also in Federalist 51:
“[T]he great security against a gradual concentration of the several powers in the same department, consists in giving to those who administer each department the necessary constitutional means and personal motives to resist encroachments of the others.”
The Legislative Branch
The executive branch must seek acquiescence from the legislative branch to operate. The clearest and simpilist safety mechanism against dictatorship is the power of the purse held exclusively by the legislative branch.
“No money shall be drawn from the treasury, but in consequence of appropriations made by law; and a regular statement and account of the receipts and expenditures of all public money shall be published from time to time.” (US Constitution, Art. I, Sec. 9)
So, the President may not spend even one penny without the authorization of Congress to do so. Without money to spend, a dictator is dead in the water. Full stop.
While this provision alone is fully adequate to prevent a dictatorship. We can keep going.
Only Congress can make laws, levy taxes and declare war. The Senate must approve a President’s nominees and any treaties he makes. Most of the powers of President must be delegated to him by act of Congrsss and can be rescinded by the same. So, without the legislative branch to raise and appropriate funds and delegate him lawful authorities, a would-be despot wouldn’t get very far.
The Judicial Branch is designed to ensure the efficient and fair execution of laws. Judicial review constrains the Executive and Legislative branches within constitutional bounds. It also restricts the President’s ability to act outside of the authorities granted him by the legislature. Further, because judges are appointed for life, it possesses a degree of independence from the other two branches in making its judgements.
The ultimate check on a tyrannical President is the people. An opportunity arises every four years for a tyrannical President to be thrown out on his ear. And if Congress doesn’t constrain him in the meantime, legislative elections every two years give voters the chance to ensure that he does. Regular elections ensure that even if a despotic President manages to capture the Legislative Branch, he cannot do so for long.
Even if a majority is willing to acquiesce to a dictator, the Constitution still has tricks up its sleeve. The system of checks and balances limits a tyranny of the majority:
“The remedy for this inconveniency is to divide the legislature into different branches; and to render them, by different modes of election and different principles of action, as little connected with each other as the nature of their common functions and their common dependence on the society will admit.”
The longer term of Senators (and originally their election by state legislatures), separates their interests from the popular whims of the moment. Further, the rules of that body, especially the filibuster, allow the minority to frustrate the will of the majority.
The electoral college system ensures that regional interests are accounted for in the election of Presidents. The electors are also empowered to ignore the popular vote altogether and vote their conscience, providing a corrective mechanism should the popular masses be hoodwinked by a demagogue.
The founders of the American Republic laid multiple layers of traps to ensnare even the most devious of aspiring tyrants. Whatever scheme a would be despot might employ, their ingenuity stands ready to frustrate it.