Competition among states. They do it all the time. States would see businesses and families leaving if their tax rate was too high. You would have a choice. Right now we have none.
Allow competition to work at the “gubmint” level.
Those same choices exist now without a sales tax. I dont see how adding a national sales tax is going to get a state like Il to lower theirs.
I just dont like a plan that forces you to rely on the hope that other entities will help you out.