Since in 1980 thru 1982, it is not even remotely likely that Barry Soetoro foresaw being a Seantor from Illinois or a presidential candidate, it is likely that he used his Indonesian citizenship as an adult to game the college netry and perhaps college tuition/scholarship programs, and to travel on an Indonesian passport. THAT constitutes a default to Indonesian citizenship as an adult. Any subsequent act to regain sloely American citizenship would constitute citizenship via statute and make him precisely ineligible for the primaries, much less the swearing in.
Pardon me for jumping in here with a thought.
Barry went back to live in Hawaii as a child at what, age 10? Even if he did nothing and remained a citizen of Indonesia, which I suspect he did just that, he had to apply and received an Indonesian passport at some point (at 16 or after?) to travel on it. No way he could travel as an Indonesian passport at 21 which was issued at the age of 10. Btw, most passport for children last only 5 years anyway.
Again, my gut hunch is that the hot paper trail should be in Indonesia.