Social Security Crisis

Bush and other proponents of eliminating Social Security have argued that the "crisis" in Social Security starts in 2018 because at that point the Social Security Administration will need to start selling off Treasury Notes in order to pay benefits. However, there seem to be only three possibilities with respect to this issue:

1. The US government will have no problem paying off the Social Security Administration's Notes. There is no problem starting in 2018.
2. The US government will be able to pay off Notes from the Bank of Japan, China, Citicorp and other such entities but the Social Security Administration and American Citizens will get shafted. I can think of no good reason for why this would be the case. Proponents of Social Security Elimination should explain why this would be, if this is the case.
3. The US government will not be able to pay off any Treasury Notes starting in 2018. In this case we have a bigger problem than Social Security and this Administration really needs to explain what is going on and why such a crisis is looming.

If there are any other possibilities, I'd very much like to know. The cases I've outlined either indicate no problem or are implausible.