Each Republican primary debate is typically sponsored by both a Republican Party organization (e.g. a state chapter of the Party) and a media outlet or two (e.g. Fox, CNN, local TV networks, newspapers).
The organizations holding the debates cannot merely invite candidates on a whim. Nor can they exclude candidates because they don't like them. For various legal reasons, the decision must be based on a set of written rules applied equally to all candidates: For example, they can have a rule that says: "The top four candidates in the next Gallup poll will be invited." The rule is neutral because it does not include or exclude a specific candidate by name.
In theory, all's fair. The reality is somewhat different. Debate organizers can set or change the rules in creative ways to ensure that certain candidates are included or excluded. More frequently it is the latter. If a candidate is considered annoying or distracting--and is not leading in the polls--it isn't difficult for a "neutral" rule to be written that results in his exclusion.
For example, in the 2008 Democratic primary, the top four candidates were Obama, Hillary, Edwards, and Bill Richardson. Only the top three had a chance of winning the nomination, but the Democrats liked that they--unlike the Republicans--had at least one Hispanic candidate competing. MSNBC's rule was that they would invite candidates who placed in the top four in any national poll; they would include the frontrunners and Bill Richardson, but no one else.
Unexpectedly, the diminutive Dennis Kucinich managed to take the fourth spot in one of the polls. Kucinich had criticized the other candidates for not being strongly against the Iraq war and not being far enough to the left. The Democratic Party establishment did not want Kucinich to participate, but the rules were the rules. MSNBC was required to invite him. Before the debate, Richardson dropped out of the race. Since Richardson wouldn't be there anyway, MSNBC changed the rules so that only the top three in any national poll would be invited. Kucinich's invitation was rescinded. Kucinich sued in Nevada state court and won. But MSNBC appealed the ruling and defeated Kucinich: The day of the debate, the Nevada Supreme Court ruled Kucinich could be excluded.
That wasn't the only time such a call was made by debate organizers during the 2008 primaries. Previously, Mike Gravel (another anti-war candidate) had put in embarrassing performances during Democratic primary debates. New rules were written that excluded Gravel alone. He was relegated to taping himself watching the other candidates debate on TV and pausing the footage to insert his own remarks.
Republican debate organizers were no less willing to tailor the rules to the circumstances. Yet another anti-war candidate, Ron Paul, was eventually excluded by new rules basing the invites on each candidate's performance in national primary polls. Paul was not able to meet the requirement. Though Paul was leading Fred Thompson in the New Hampshire polls and beat Rudy Giuliani in the delegate count, Thompson and Giuliani polled well nationally and were included in the debates.
Debate moderators are also able to show some favoritism during the debates themselves. They tend to ask more questions to the more well-known candidates. Some lesser-known candidates may only get a few minutes of airtime during a two-hour debate.
Debate invites will be crucial for those struggling to boost their name recognition. Elephant Watcher has identified Herman Cain as one to watch in this regard: He may or may not be invited. His poll numbers are low (so far) and he has never held elective office. But his poll numbers may be just high enough in Iowa, and the debate organizers may feel it is a good idea to include at least one black candidate in the debates. Cain's fate in the race may well be decided by the debate organizers.
