In fact, to oversimplify a bit, I can boil the essence of the legal analysis down by analogy to a conversation.
Indonesia: “Only an Indonesian citizen can get an Indonesian passport from me. And if you are claiming to be an Indonesian citizen, you cannot be a citizen of any other country.”
Obama: “Hi, my name is Barack Obama. I would like to obtain or renew an Indonesian passport. I am claiming to be an Indonesian citizen. Therefore I am not a citizen of any other country.”
Uncle Sam: “Say, I was standing over there and overheard your conversation. On our records, you are a United States citizen. I just heard you state that you, as an adult and voluntarily, claim to be an Indonesian citizen and are not a citizen of any other country. By your statement you have made a choice of allegiance to Indonesia, and have forsworn allegiance to the United States. That is sufficient under my law to relinquish your United States citizenship.”
Ahhhh, I think I might get what you are saying now!
Yes, it is entirely possible that if the United States wanted to get rid of Barack Obama, which they DO NOT and WON'T because he is President, they could DEFINITELY try using something like that as their reasoning. Like getting Al Capone put away for tax evasion.
Although it could well be that the form he filled out at 19 to renew his Indo pass didn't contain ANY swearing of allegiance but was instead just your basic form renewing a document. As it is here. Show us your old pass, where do you live, let's see your ID, bla bla bla.
It's a moot legal point because the State Dept definitely will not be pursuing ANY way to remove Barack Obama's citizenship, no matter what he swore to the Indos. Even Adam Gadahn was broadcasting Al Qaida's wishes for some time before he lost his USA citizenship.