Can congress cut our SS?

Yes. The so called trust fund assets are owned by the federal government. The tax collections are too. The benefit levels are determined by formulas in law passed by Congress. That law and those formulas have been amended more than once already. The retirement age has been increased. What is that but a decrease in benefits?

What Congress has done it can undo, partially or completely. Unlike a genuine trust, where the trustee doesn't own the assets but merely manages them on behalf of another party, the federal government owns the S.S. trust fund lock, stock and barrel. Your benefits depend solely upon a formula in law that can be changed like any other law.

The government wrote ITSELF those worthless IOUs, not you. No other party has the slightest legal claim to them.