Conversation so far:
What are the most important US supreme court cases?
Marbury v. Madison, 1803 (4-0 decision) ...McCulloch v. Maryland, 1819 (7-0 decision) ...Dred Scott v. Sandford, 1857 (7-2 decision) ...Plessy v. Ferguson, 1896 (7-1 decision) ...Korematsu v. United States,
What did Plessy v. Ferguson establish?
Plessy v. Ferguson was a landmark 1896 U.S. Supreme Court decision that upheld the constitutionality of racial segregation under the “separate but equal” doctrine. The case stemmed from an 1892 incident in which African-American train passenger Homer Plessy refused to sit in a car for blacks.

Question: How about Marbury vs Madison?
Self-contained rewrite: What did the Marbury vs Madison case establish?