Now why would a US citizen have a passport from another country?
Lots of US citizens hold passports from other countries. I have friends that have both a US passport, and a passport from Israel, Canada, New Zealand, Australia or Ireland (they have a US passport and one from those other countries - more than one friend). The only thing you have to remember is to use the same passport on entering another country and returning to the US, or things can get quite sticky.
Better question: Where’s the “facts” and evidence that this occurred. As with most (all) of the complaint, it’s based on the rumors put forth primarily by NoQuarterUSA and TexasDarlin’s websites.
I think this is a red herring and will backfire — by making ANY questions/challenges to Obama’s brackground suspect.