The current rules don't require the brokers to fix the trades by buying shares to cover their short positions after 13 days, they merely say that if the trades aren't fixed, the broker can't do any more short-sales in that securitywithout borrowing or arranging to borrow the stock.
Hence, virtually all benefits can be paid out of revenues without having to borrow more money from the public, and the relatively small Social Security deficits expected during the coming decade (3% of payroll tax revenues) can and should be covered by earmarking enough general revenues to redeem the Trust Fund IOUs Congress left behind when it looted Social Security during the past 25 years.