Answer:
Judicial Review
Explanation:
Acts of the legislature (which is congress), the executive (presidency), state governments and other arms of government are subject to judicial review by the courts, most especially the supreme court. In other words, it is up to the supreme court to determine what is constitutional and what is unconstitutional.
A prominent example of a judicial review by the supreme court is the landmark case Roe v. Wade in 1973. The landmark judgement upended several state laws that prevented pregnant women from having abortions. The supreme court ruled that it was unconstitutional for the states to restrict pregnant women from having abortions as it violated their constitutional right of privacy.