I honestly don't understand that. You can trade U.S. treasury notes on the market. Or to make it easier, you can buy and sell shares in ETF's like TLT or mutual funds like PRULX that buy and sell U.S. treasuries like stocks. The fund managers hold onto them to collect dividends, or sell them whenever treasury rates go down (which always make the sell price of a treasury note go up because your existing treasury note collecting at a higher rate has more value than a new treasury note at a lower rate).
So is there a law saying that whatever treasuries the SS fund buys has to always be held to maturity and never sold like other treasury investors do?
Watch this magic trick carefully:
https://www.ssa.gov/oact/progdata/specialissues.html
“The trust funds now hold only special issues”
So what are these “special issues”?
Follow the pea while I move my hands quickly:
https://crsreports.congress.gov/product/pdf/IF/IF10564
“Section 201 of the Social Security Act (42 U.S.C. §401)
requires the managing trustee of the Social Security trust
funds (the Secretary of the Treasury) to invest Social
Security tax revenues in special “nonmarketable” federal
public-debt obligations called special issues”
In other words—Ponzi scheme.