Iowa constitution
Article IV
Section 4

The nominees for governor and lieutenant governor jointly having the highest number of votes cast for them shall be declared duly elected. If two or more sets of nominees for governor and lieutenant governor have an equal and the highest number of votes for the offices jointly, the general assembly shall by joint vote proceed, as soon as is possible, to elect one set of nominees for governor and lieutenant governor. If, upon the completion by the general assembly of the canvass of votes for governor and lieutenant governor, it appears that the nominee for governor in the set of nominees for governor and lieutenant governor receiving the highest number of votes has since died or resigned, is unable to qualify, fails to qualify, or is for any other reason unable to assume the duties of the office of governor for the ensuing term, the powers and duties shall devolve to the nominee for lieutenant governor of the same set of nominees for governor and lieutenant governor, who shall assume the powers and duties of governor upon inauguration and until the disability is removed. If both nominees for governor and lieutenant governor are unable to assume the duties of the office of governor, the person next in succession shall act as governor.