There are times when the President refuses to spend money that has been appropriated by Congress. Which principle does this align with? My options are popular sovereignty checks and balances separation of powers and federalism

Impoundment is an act by a President of the United States of not spending money that has been appropriated by the U.S. Congress. Thomas Jefferson was the first president to exercise the power of impoundment in 1801. ... The president's ability to indefinitely reject congressionally approved spending was thus removed.

separate but equal was a legal doctrine in united states constitutional law according to which racial segregation did not violate the fourteenth amendment to the united states constitution, which guaranteed "equal protection" under the law to all people. under the doctrine, as long as the facilities provided to each race were equal, state and local governments could require that services, facilities, public accommodations, housing, medical care, education, employment, and transportation be segregated by race, which was already the case throughout the states of the former confederacy. the phrase was derived from a louisiana law of 1890, although the law actually used the phrase "equal but separate

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