THERE IS NO "FUND"
The "fund" is US treasuries HELD by the SSA.
ALL social security benefits are PAID by general revenue, and the amount collected by the FICA portion of taxes is less than the payments (which are considered part of general revenue).
By my reckoning, given the massive deficits, that means it is ALREADY insolvent--its dedicated taxes can no longer pay its benefits, and the NPV of its liabilities is already even larger than the current publicly held federal debt.
What they mean when they project this "insolvency" is the date when EVEN IF the federal government can pay the SSA runs out of treasuries to reclaim.
It's a double-ponzi scheme...not only is it paying out more than it takes in, but it's meager dedicated taxes have been "borrowed" as well. (one of the reasons for the fake "surplus" in the Clinton years)
Only in government can you spend more than you receive in income and still consider it a surplus.