No, the borrowing started as soon as people were told that they could expect to get anything back for the money they put in. And that happened even before the lockbox was supposedly raided.
The fundamental problem with Social Security isn't that the "trust fund" is invested in government bonds, but rather that only a small portion of the money which is "invested" goes into the trust fund. The only ways Social Security manages to maintain the illusion of generating a positive rate of return are (1) by having people pretend they only put in half of what they do, thereby getting an extra guaranteed "100%" rate of return; (2) by confiscating almost all of the contributions of people who die prior to retirement; (3) by spiralling deeper into the debt cycle.
Any accountant who tried anything like that with a private retirement firm would be in prison, and for good reason.
We can agree that you get more for your effort by simply putting cash in Mason jar and hiding it in your closet. Current retirees are receiving what, approximately 60% of what they paid into the system? It is an accounting farce. I do do better placing the same amount deducted from my pay into a simple savings account at the bank. I really learned how much we pay for SS when I worked as a self-employed consultant. Income tax was small sompared to the SS extortion.