The underlying principle incorporated in the writing of the American Constitution is of the division of authority and powers which detail the sharing of various powers and functions of government to separate be independent from the branches of the federal system in order to prevent all the branches, department and division being controlled by any potentially tyrannical political faction. But, to the way of thinking of the Framers of the Constitution, the long-term survival of free popular government would require more than simply a purely formalistic separation of governmental functions and powers into completely independent organizational jurisdictions.
Ruthless and unprincipled incumbents in one or another of the several different departments and levels of government could usurp the powers and authority of the other branches and levels from periodically, and this would eventually result in an oppressive and dictatorial concentration of powers unless the select few in the other parts of the government were given the needed reasons and constitutional means to resist the exceeding of power limits by the others. “Ambition must be made to thwart ambition. The interest of the officeholder must be associated with the constitutional rights of the individual and should be in accordance with the constitution of the country.
The Writers of the constitution agreed that there was a legal requirement for the Constitution to include a readymade set of “checks and balances” which afforded the required protection for each branch to defend itself against usurping of on its independence and authority by the others. In most cases, this balance of power is purely negative, usually taking the form of some special constitutional grant of authority for one branch to say “no” to at least some of the specific decisions of the other branches in their own fields of specialization and then make it stick. The two houses of Congress may finally agree on a compromise to pass or repeal a law, but it can be vetoed by the President.
President and Congress can agree on passing a law, but if the federal judiciary declares it to be unconstitutional the courts can refuse to treat the law as legitimate or be obeyed. The courts can issue orders and for particular individuals to act or abstain from acting in particular ways, including public officials, but the power of the law enforcement agencies in the executive branch is needed to enforce them if the individuals in question decides not to obey the courts injunctions.