18. what is the significance of john marshall's ruling in marbury v madison? provide examples of the impact of this ruling

 The Supreme Court has the right of judicial review and can  declare laws of Congress unconstitutional.  

Explanation:

It was sort of a roundabout way in which the principle of judicial review was asserted by the Supreme Court in the case of Marbury v. Madison. William Marbury had been appointed Justice of the Peace for the District of Columbia by outgoing president John Adams -- one of a number of such last-minute appointments made by Adams.  When Thomas Jefferson came into office as president, he directed his Secretary of State, James Madison, not to deliver many of the commission papers for appointees such as Marbury.  Marbury petitioned the Supreme Court directly to hear his case, as a provision of the Judiciary Act of 1789 had made possible.  The Court said that particular provision of the Judiciary Act was in conflict with Article III of the Constitution, and so they could not issue a specific ruling in Marbury's case (which they believed he should have won).