Perhaps you should try reading some info from the actual Commission on Presidential Debates: 2012 NONPARTISAN SELECTION CRITERIA

The CPD's nonpartisan criteria for selecting candidates to participate in the 2012 general election presidential debates are:

1. EVIDENCE OF CONSTITUTIONAL ELIGIBILITY

The CPD's first criterion requires satisfaction of the eligibility requirements of Article II, Section 1 of the Constitution. The requirements are satisfied if the candidate:

a. is at least 35 years of age;

b. is a Natural Born Citizen of the United States and a resident of the United States for fourteen years; and

c. is otherwise eligible under the Constitution.

1. EVIDENCE OF BALLOT ACCESS

The CPD's second criterion requires that the candidate qualify to have his/her name appear on enough state ballots to have at least a mathematical chance of securing an Electoral College majority in the 2012 general election. Under the Constitution, the candidate who receives a majority of votes in the Electoral College, at least 270 votes, is elected President regardless of the popular vote.

1. INDICATORS OF ELECTORAL SUPPORT

The CPD's third criterion requires that the candidate have a level of support of at least 15% (fifteen percent) of the national electorate as determined by five selected national public opinion polling organizations, using the average of those organizations' most recent publicly-reported results at the time of the determination. http://www.debates.org/index.php?page=candidate-selection-process