Why? There's nothing in the Constitution that forbids referendums. I'd imagine it'd be tricky for the current Congress to try and bind the hands of a future c

Why? There's nothing in the Constitution that forbids referendums. I'd imagine it'd be tricky for the current Congress to try and bind the hands of a future congress i.e. The current Congress creates a referendum that compels the next Congress to pass a certain bill and the President to sign it. There's no reason the current Congress couldn't pass a bill and the President sign it into law that says the current Congress will act in accordance with the result of referendum. The congress could even pass the enabling of the referendum and the enabling of the result of the referendum without the consent of the President - if they have the votes to override the President's veto. It'd be odd to be sure but I don't see why they can't do it.