He might be a citizen but not a natural born citizen.
If he were born in Kenya, his mother was too young by 3 months to pass on citizenship, so he would have had to have been naturalized.
If he were born in Hawaii, he would still have been a dual citizen, thus probably disqualified as both parents needed to be U.S. citizens.
This is for the courts to decide. And hopefully they will.
Being a dual citizen would not disqualify him so long as he retained his US citizenship. And since Hawaii is US territory, he would be a citizen by birth regardless of the status of his parents.