the "unwritten constitution" consists of certain practices and traditions usually occurring in the government even though they were not included in any document. Some examples of the unwritten constitution are a two-party political system and the presidential cabinet.
Spoils of victory (jacksons partisan victory for "the people" ushered a change in the filling of government jobs), Kitchen Cabinet (which was Jeffersons Cabinet), Nullification Crisis (At the time of Jacksons inauguration) I think. :)
Legislative - Congress can override a Presidential veto, or refuse to declare war, or block funding for Federal programs; the Senate can refuse to confirm Presidential cabinet nominees or Federal judges Judicial - the Supreme Court can find an executive order unconstitutional
There are 18 people including the vice president. The list consists of (1) the VP, (2) the speaker of the House, (3) the president pro tempore of the Senate, followed by the 15 cabinet members in order of the creation of their departments.