Three safeguards against abuse of presidential power are Congress, Supreme Court, and the ability of Congress to impeach.
United States Congress
Supreme Court of the United States
A supreme court is the highest court within the hierarchy of many legal jurisdictions. Other descriptions for such courts include court of last resort, instance court, judgment court, apex court, and highest court of appeal. Broadly speaking, the decisions of a supreme court are not subject to further review by any other court.
In a few places, the court named the "Supreme Court" is not in fact the highest court; examples include the Supreme Court of the State of New York and the former Supreme Court of Judicature of England and Wales. The highest court in some jurisdictions is not named the "Supreme Court", for example, the High Court of Australia; this is because decisions by the High Court could be appealed to the Privy Council.
The Supreme Court of the United States (first abbreviated as Scotus in 1879) was established pursuant to Article III of the United States Constitution in 1789 as the highest federal court in the United States. It has ultimate (and largely discretionary) appellate jurisdiction over all federal courts and over state court cases involving issues of federal law, plus original jurisdiction over a small range of cases. In the legal system of the United States, the Supreme Court is the final interpreter of federal constitutional law, although it may only act within the context of a case in which it has jurisdiction.
Constitutional law is the body of law which defines the relationship of different entities within a State, namely, the executive, the legislature, and the judiciary.
Not all Nation States have codified Constitutions, though all such states have a jus commune, or law of the land, that may consist of a variety of imperative and consensual rules. These may include customary law, conventions, statutory law, judge-made law or international rules and norms.
Separation of powers under the United States Constitution
Congressional oversight refers to oversight by the United States Congress on the Executive Branch, including the numerous U.S. federal agencies. Congressional oversight refers to the review, monitoring, and supervision of federal agencies, programs, activities, and policy implementation. Congress exercises this power largely through its congressional committee system. However, oversight, which dates to the earliest days of the Republic, also occurs in a wide variety of congressional activities and contexts. These include authorization, appropriations, investigative, and legislative hearings by standing committees; specialized investigations by select committees; and reviews and studies by congressional support agencies and staff.
Congress’s oversight authority derives from its “implied” powers in the Constitution, public laws, and House and Senate rules. It is an integral part of the American system of checks and balances.
Separation of powers is a political doctrine originating in the writings of Montesquieu in The Spirit of the Laws where he urged for a constitutional government with three separate branches of government. Each of the three branches would have defined powers to check the powers of the other branches. This idea was called separation of powers. This philosophy heavily influenced the writing of the United States Constitution, according to which the Legislative, Executive, and Judicial branches of the United States government are kept distinct in order to prevent abuse of power. This United States form of separation of powers is associated with a system of checks and balances.
During the Age of Enlightenment, philosophers such as John Locke advocated the principle in their writings, whereas others, such as Thomas Hobbes, strongly opposed it. Montesquieu was one of the foremost supporters of separating the legislature, the executive, and the judiciary. His writings considerably influenced the opinions of the framers of the United States Constitution.
The term crime does not, in modern times, have any simple and universally accepted definition, but one definition is that a crime, also called an offence or a criminal offence, is an act harmful not only to some individual, but also to the community or the state (a public wrong). Such acts are forbidden and punishable by law.