The Supreme Court issued a decision in North Carolina Department of Revenue v. The Kimberley Rice Kaestner 1992 Family Trust—and it’s unanimous. The Court ruled a trust beneficiary’s residence is not sufficient on its own for a state to tax a trust’s undistributed income.
The Due Process Clause is found in the 14th Amendment and states, in part: "No state shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any state deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws".