Illegitimate, because Mama Obama was not legally married to Papa Obama. He was already married to a lady (possibly two) in dear old Kenya. That enabled her to get rid of the wife-beating drunkard in a hurry when she had to. So, the worst that could be said about BHO is that he is a a dual citizen of Kenya and the US, or at least eligible for Kenyan citizenship on top of his American status. Hell, this weird, sweet-talkin' Chicago commie race-pimp might even be a triple citizen, depending upon whether or not Mama Obama's replacement husband, the Indonesian Soetoro, adopted the cute little rascal.
The COLB could be phony as hell, but still quite beside the point.
the question becomes WHY would they prefer to obfuscate rather than playing it straight?