A consumption tax is the only tax that would be Constitutionally defensible. Far superior to any other system. The premier consumption tax plan that gained any support is the "FairTax".
There are problems with the plan as it stands, and their "solutions" themselves present problems rather than solutions.
These problems are not insurmountable.
The problems arise from the idea of a "prebate" (why not just not levy a tax on "necessities" in the first place?) and the idea of the plan being a replacement for the unconstitutional income tax and therefore must be "revenue neutral" (e.g. produces a revenue stream equal to the current income tax levels) which is completely undefensible.
Spending is the problem.
Nevertheless...the fairtax videos below explain very well how a consumption tax would work. Far superior to an income tax...including the "flat tax". (the problem with the flat tax is simple...it STILL an income tax. The Government has no business knowing anything about your income...period)