Sure it can. Congress created the Federal Reserve system, Congress can take it away. History tells us that Congress shouldn't be involved in fine-tuning the money supply, but maybe one day things will change. Most countries have central banks now and it seems to work pretty well so far.
>>They back our money with nothing and charge interest on that.<<
They repay interest in excess of expenses to the Treasury. As for whether the money supply is backed, I think our money supply is backed, for the most part, by collateral like property (mortgages) and businesses (commercial paper).