You can’t really say they dipped into it. It’s funds are the general fund. Social Security deductions simply go into the general fund. They are in a constant state of tapping that.
If they would simply invest Social Security funds, they’d fund Social Security easily.
Still, those funds should be owned by the citizen outright, invested and always theirs. They wouldn’t be able to tap them until a date to be specified, but the funds should be placed somewhere and individual accounts be able to be watched by the citizen.
While the unified accounting instituted during the 80's effectively co-mingles all the funds, there is an accounting that tracks the difference between the revenue collected by the payroll tax, and the benefits paid. When it was positive, the surplus went into the Social Security Trust Fund. It's in the equivalent of long-term US Treasury Bonds.
But, in the past few years, the surplus disappeared, thanks to the Great Recession and a wave of early retirements. So, now the difference is being made up by withdrawing from the Trust Fund. Those bonds are being redeemed, and the funds come from general revenue (which means they are effectively converted into US Treasury bonds and sold on the open market).
The problem: the Trust Fund is expected to be exhausted in 2033, and there will be only enough taxes to pay 77% of benefits. The "deadline" has been getting earlier every year, I remember when it was 2041 not so long ago. And frankly, since I think their assumptions are too optimistic, I think the real date will be in the late 2020's, if not even earlier.
You can’t really say they dipped into it.
Why did the so called lock box come about for SS funds?.