Reddit mentions of The Imperiled Union: Essays on the Background of the Civil War

Wow, this is a pretty broad question that can probably be best answered by any one of dozens of general histories of the United States.

Off the top of my head, some of these challenges would be:

• Marbury v. Madison (1803), wherein the Supreme Court arrogated to itself the extra-Constitutional power of judicial review.
  
• The Louisiana Purchase (1803), wherein the Executive purchased and acquired territory from another nation without the consent of Congress.
  
• The Burr "Conspiracy" (1806), wherein the President declared publicly that Aaron Burr was guilty of treason before he'd even been indicted by a grand jury. Furthermore, Jefferson attempted to assert that the language in the Constitutional definition of "treason" did not apply; Chief Justice Marshall said it did, and Burr was promptly acquitted.
  
• The Nullification Crisis (1832), wherein a state (South Carolina) attempted to arrogate for itself the power of deciding which Federal laws were applicable to itself. The attempt at nullifying the Tariffs of 1828 and 1832 ultimately failed, due to President Jackson's threat of force as well as a compromise tariff bill.
  
• The Dred Scott case (1857), in which Chief Justice Taney made the legally (and logically) dubious ruling that the Federal government's ability to regulate the territory and property of the various states under Article IV of the Constitution only applied to those states which were part of the U.S. as of the time of the ratification of the Constitution. A legal victory for the slave states, but the outrage it precipitated in the North would prove crucial in building popular support for the prosecution of the war against the secessionists.
  
  SOURCES:
  
  Stampp, Kenneth. The Imperiled Union: Essays on the Background of the Civil War. Oxford University Press, 1981.
  
  Wills, Garry. Negro President: Jefferson and the Slave Power. Houghton Mifflin Harcourt, 2003.
  
  Newmyer, R. Kent. The Supreme Court Under Marshall and Taney. Harlan Davidson, 2006.