Marbury v. Madison was an important case because it was the first time that the U.S. Supreme Court applied judicial review to a case. Judicial review is where the federal courts have the power to void acts from Congress that differ from that of the Constitution.
The 1800 election resulted in Thomas Jefferson's Democratic-Republican party defeating John Adams Federalist Party. In his last few days of presidency, Adams appointed justices of peace for DC. These commissions were approved by the Senate, signed by Adams, and had the seal of the government of the letters. However, these commissions were never delivered