The case of Planned Parenthood v. Casey exemplifies the idea that the Constitution is the supreme law of the land because it is a case in which a state law is made invalid because the Supreme Court of the United States says that the law conflicts with the Constitution. Because the Constitution is the supreme law of the United States, it overrules any law made by any state. This is what happened in Planned Parenthood v. Casey.
In this case, the state of Pennsylvania had enacted laws that placed restrictions on women’s right to get abortions. In 1973, the US Supreme Court had said (in Roe v. Wade) that there is a constitutional right to abortion. In Casey, the Court had to decide whether the Pennsylvania law violated the constitutional right to abortion announced in Roe. In the end, the Court decided that it did and the law was invalidated. This exemplifies the idea that the Constitution is the supreme law of the land because a state law was thrown out when the Supreme Court ruled that it violated the Constitution.