Assuming for the sake of argument that he was an Indonesian citizen, that is a determination of the Indonesian government. In the eyes of the Indonesian government, he would not be a U.S. citizen; if arrested, he would have no right to be represented by the U.S. embassy, and he would no be allowed to travel into or out of Indonesia on a U.S. passport.
That determination of the Indonesian government does not overrule the U.S. law on U.S. citizenship.
There is a common and mistaken belief that "dual citizenship" is some sort of formal status universally recognized around the world. It just ain't so. A dual citizen is someone who is a citizen of two countries under the law of each. One government's opinion is not binding on the other.
If you're a U.S. and Israeli citizen, for example, you must travel into and out of the U.S. on an U.S. passport. If you're arrested in the U.S., you have no right to contact the Israeli embassy. If you're arrested in Israel, you will not be extradited to the U.S. or any other country, because that is the policy of the Israeli government.
There was a war. Are you old enough to remember?
Yes. There was a war. That fact has no bearing on the citizenship status of Barack Obama or anyone else.
It was not an American vacation spot in 1981
Obama went somewhere few Americans went. That act did not strip him of his citizenship.
I still say you must be too young to remember the mess that was Pakistan in 1981. No American went there on vacation.
Back of a limo with Larry Sinclair?