The principle of checks and balances in the U.S. Constitution has been a fundamental component of American democracy, designed to prevent the concentration of power in one branch of government. Throughout history, various presidents have tested this system, such as Donald Trump with his executive orders and denigration of the judiciary, and Andrew Jackson with his opposition to the national bank. Abraham Lincoln also challenged this principle during the Civil War by suspending habeas corpus, while Franklin D. Roosevelt faced resistance with his New Deal and attempted court-packing scheme. Despite these challenges, the system has often held, with Congress and the courts asserting their roles in balancing presidential power, as seen in the Watergate scandal and the creation of the United Nations and NATO post-World War II.

The principle of checks and balances is embedded in the U.S. Constitution, creating three coequal branches of government to prevent any one branch from gaining too much power, a system tested by President Donald Trump through executive orders and agency reductions.

Historical examples of checks and balances include President John Adams' last-minute appointments, which led to the landmark Marbury v. Madison case establishing the Supreme Court's role in interpreting congressional acts and executive actions.

During the Civil War, Abraham Lincoln suspended habeas corpus, a move deemed illegal by the Supreme Court, yet Congress retroactively supported Lincoln, highlighting the tension between executive power and legal constraints during wartime.

Franklin D. Roosevelt's New Deal faced opposition from a conservative Supreme Court, leading him to propose expanding the court, a move criticized as a 'court-packing scheme,' reflecting the ongoing struggle between legislative, executive, and judicial powers.

The Watergate scandal demonstrated the effectiveness of checks and balances, as congressional hearings and a Supreme Court ruling against Nixon's use of executive privilege led to his resignation, showcasing the system's capacity to hold presidents accountable.

The creation of the United Nations and NATO after World War II, with Senate support, marked a shift from the rejection of the League of Nations post-World War I, illustrating the evolving role of Congress in foreign policy decision-making.

The Affordable Care Act exemplifies the interplay between the branches, as the Supreme Court upheld parts of the law while restricting federal power over states, demonstrating the judiciary's role in checking legislative and executive actions.