Heidi Li Feldman of The Denver Group has an awesome post on the DNC Convention rules ("Call to the Convention" published by Democratic National Party published February 2007). Must read!
http://heidilipotpourri.blogspot.com/2008/07/dnc-convention-rules-essential.html--snippet--
The Call to the Convention serves as a blueprint or governance document specifying how the the convention will be convened and what will happen there.
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Section VI defines the term "Presidential Candidate" for purposes of the Convention. Here is that provision in its entirety:
The term “presidential candidate” herein shall mean any person who, as determined by the National Chairperson of the Democratic National Committee, has accrued delegates in the nominating process and plans to seek the nomination, has established substantial support for his or her nomination as the Democratic candidate for the Office of the President of the United States, is a bona fide Democrat whose record of public service, accomplishment, public writings and/or public statements affirmatively demonstrates that he or she is faithful to the interests, welfare and success of the Democratic Party of the United States, and will participate in the Convention in good faith.
Note: the "plans to seek the nomination" does not state a deadline for when a candidate must announce that he or she so plans. So any candidate who meets the other guidelines in Section VI and announces prior to the convention's start that she or he is seeking the nomination qualifies as a "Presidential candidate" for purposes of the Call. As of today, July 25, Senator Obama is the only person who is in this position. As of August 1 or August 15 or August 20 (I'm just naming random dates before the start of the convention), others may have thrown their hat in the ring. John Edwards, for example, could do so.
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Finally, subsection 7 defines what happens after the nomination speeches are given:
7. Roll Call for Presidential Candidate:
a. After nominations for presidential candidates have closed, the Convention shall proceed to a roll call vote by states on the selection of the presidential candidate. The roll call voting shall follow the alphabetical order of the states with the District of Columbia and Puerto Rico and the territories treated as states for the purpose of the alphabetical roll call.
b. A majority vote of the Convention’s delegates shall be required to nominate the presidential candidate.
c. Delegates may vote for the candidate of their choice whether or not the name of such candidate was placed in nomination. Any vote cast other than a vote for a presidential candidate meeting the requirements of Article VI of this Call and Rule 12.K. of the 2008 Delegate Selection Rules shall be considered a vote for “Present.”
d. Balloting will continue until a nominee is selected. The nominee shall become the candidate of the Democratic Party of the United States for the Office of President upon the conclusion of his or her acceptance speech.
Note: it is because of subsection 7(c) that the difference between being a nominee and simply being on the ballot makes a difference. If a candidate is not a nominee at the time of the roll call, votes for that candidate simply count as "present".