According to Marshall, why does the Supreme Court have the right to rule on whether a law is constitutional?

Because a law cannot go above and beyond your constitutional rights. This stating that the Supreme Court will determine if the ruling is constitutional or not. Your rights can not be violation even by the government all of your rights as a citizen of the United States are protected by the Constitution. / Bill of Rights.

Declaring the Constitution "superior, paramount law," the Supreme Court ruled that when ordinary laws conflict with the Constitution, they must be struck down.