Politico reports that “Schultz said on his show Tuesday evening that he believes North Dakota law holds that a candidate would have to be a resident for the past five years to run, and he hasn’t been living in the state.”
Whether or not North Dakota has such a law applicable to state candidates, it cannot constitutionally be applied to candidates for the U.S. Senate or House, where the U.S. Constitution sets the sole requirements. Here’s a footnote from our election law casebook, page 549:

Under the Constitution’s Qualifications Clauses, members of the United States Senate and the House of Representatives must be residents of the state they represent. See U.S. Const., Art. I, s2, cl. 2; s3, cl. 1. Numerous courts have struck down state statutes attempting to impose additional requirements such as that a candidate for the House be a resident of the Congressional district. See Daniel H. Lowenstein, Are Congressional Term Limits Constitutional?, 18 Harvard Journal of Law and Public Policy 1, 43-44 (1994) (collecting cases); see also Schaefer v. Townsend, 215 F.3d 1031 (9th Cir. 2000), cert denied sub nom. Jones v. Schaefer, 532 U.S. 904 (2001), in which the Ninth Circuit held that “California’s requirement that candidates to the House of Representatives reside within the state before election violates the Constitution by handicapping the class of nonresident candidates
who otherwise satisfy the Qualifications Clause.”