What principle ensures congress and the president abide by the constitution?

The principle that ensures Congress and the President abide by the Constitution is called "checks and balances." This system divides government powers among three branches: the legislative, executive, and judicial. Each branch has specific responsibilities and can limit the powers of the others, ensuring that no single branch becomes too powerful. Additionally, the judiciary interprets the Constitution and can declare laws or executive actions unconstitutional, reinforcing adherence to constitutional principles.