Final answer:
The 1857 Supreme Court case that is regularly cited as the worst Supreme Court decision in U.S. history is Dred Scott v. Sandford. The case held that Black Americans could not be citizens, declared the Missouri Compromise unconstitutional, and is considered a catalyst of the Civil War.
Step-by-step explanation:
The 1857 Supreme Court case that is regularly cited as the worst Supreme Court decision in U.S. history is Dred Scott v. Sandford. In this case, the Supreme Court held that Black Americans could not be citizens, declared the Missouri Compromise unconstitutional, and ruled that Congress had no authority to limit the spread of slavery into American territories. This decision was a catalyst for the Civil War as it further heightened tensions between the North and the South over the issue of slavery.