Widgets are manufactured wholly from raw materials mined and processed in the state of Green. The only two manufacturers of widgets in the United States are also located in that state. However, their widgets are purchased by retailers located in every state. The legislature of the state of Green is considering the adoption of a statute that would impose a tax solely on the manufacture of widgets. The tax is to be calculated at 3% of their wholesale value. Which of the following arguments would be LEAST helpful to the state in defending the constitutionality of this proposed state tax on widgets? 
At the time widgets are manufactured and taxed they have not yet entered the channels of interstate commerce. The economic impact of this tax will be passed on to both in-state and out-ofstate purchasers of widgets and, therefore, it is wholly nondiscriminatory in its effect.  Because of the powers reserved to them by the Tenth Amendment, states have plenary authority to construct their tax system in any manner they choose.  A tax on the manufacture of widgets may be imposed only by the state in which the manufacturing occurs and, therefore, it is not likely to create the danger of a multiple tax burden on interstate commerce. 