Hi bjorn14,
The US Constitution does require citizenship status for U.S.Senators. Article 1, Section 3, Clause 3: "No Person shall be a Senator who shall not have attained to the Age of thirty Years, and been nine Years a Citizen of the United States, and who shall not, when elected, be an Inhabitant of that State for which he shall be chosen."
Green cards do not provide citizenship but grant, instead "Lawful Permanent Residence" According to the US Immigration web site,"United States citizenship is one step beyond permanent residency (Green Card). US citizenship gives an individual the maximum rights available in the United States."
State Senators (at least in my state), need only be citizens, as you stated, but there is a higher standard for U.S. Senators. So, it seems to me, that Mr. Keyes may have been twice-wronged by Barack Obama in his campaigns. Surely no court can legitimately deny Mr. Keyes his "standing"....
Gizmos, are you implying that a citizen is not the same as a citizen of the United States?
My bad, relying on my memory from my college freshman-year American Government which was many moons ago. I knew a Sen. did not have to be a NBC.