The Stenbach theorem is a principle of conservative political philosophy originally conceived by Edward Stenbach. It is based on elitist government principles and applies to the elitist and perfectionist nature of the Executive Branch.
The theory states that, "If an individual holds office as two Executives offices, their effort will be split so that the competitive nature of the election of Executives will make it easier and more practical for a new applicant to prevent them from continuing to hold one of the offices." In essence, the theory can be explained by stating that if an Executive is (illegally and undesirably) holding two offices in the Executive Branch, then their energy is split rough 50% between both offices, not 100% into one, so someone who is able to devote 100% of their energy to one office could easily out-compete them and prevent them from continuing to hold that office.
Furthermore, the individual acting as two Executives is likely to be impeached before competition due to devoting significantly less energy/time to both offices, which should be notable in a branch where every Executive is devoting 100% to their single office.
If John is in office as Head of Research and as Head of Naturalization, he cannot devote 100% of his energy/time to both. He has to devote about 50% of his total energy/time to each. Because the Executive Branch is designed to be highly competitive, another applicant with roughly the same skill set as John could easily compete for the position and drive John out of office.
Conservatives argue that, when citizenship fosters a competitive environment, this is a solution to Executives undermining the system and trying to hold more than one office and vote. In the long-run, they state, this will be effective in promoting Executive excellence and preventing individuals from attempting to get more than one seat. Furthermore, in combination with modern techniques used to verify a singular identity it would be impossible, in a competitive system, to have more than one office.