When there was like 20 candidates in the race it made sense then to limit the race to the top tier but now that they are down to only 3 candidates, what would it hurt including Kucinich?

Rep. Dennis Kucinich won’t be taking part in MSNBC’s debate in Las Vegas on Tuesday. It certainly won’t be the first time that Kucinich was excluded from a recent Democratic debate. But the difference is Kucinich was initially invited, and had met the criteria, for the MSNBC debate. Then, MSNBC changed the criteria and told Kucinich he was uninvited.
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According to the Los Angeles Times, the original criteria for the debate called for the inclusion of the top four democratic candidates in national polling. With Bill Richardson dropping out of the race last week, that moved Kucinich to fourth place in polls. NBC decided to change the criteria, featuring the top three Dem. candidates: Sen. Hillary Clinton, John Edwards and Sen. Barack Obama.