That solves any Commerce Clause violation---uniformity prevents double taxation

Perhaps the most important Commerce Clause inquiry post-Wynne is whether a tax regime achieves internal consistency.145 The internal consistency test assumes that every state has adopted an identical tax regime and looks to whether such a scenario would place interstate commerce at a disadvantage compared to intrastate commerce.146 Importantly, even if a tax regime would otherwise be internally inconsistent, a state can cure the constitutional defect with a credit mechanism.147 An exit tax should satisfy internal consistency if it includes in the tax base only the income and gain that accrued while the taxpayer was resident in the state and that was not properly sourced to another state. If every state adopted such a regime there would be no risk of double taxation. To ensure that the exit tax regime tailors its tax base in such a manner, the tax regime must implement a credit or exemption mechanism. As discussed further in Section IV.C, when determining the tax base, the regime should allow a credit for taxes paid on income properly sourced to other states, and should provide either a basis stepup or credit for exit taxes paid to prior states of residence.148 These principles should ensure that the exit tax base consists only of income and gain that accrued while the taxpayer was a resident of the departure state, thus satisfying internal consistency.