If the Constitution was bringing into existence a government of unlimited or omnipotent powers, then there would have been no point in enumerating a few limited powers. In that event, the Constitution would have called into existence a government with general, unlimited powers to do whatever was in the interests of the nation.
If the Constitution had proposed a government of omnipotent powers, there is no way the American people would have accepted it, in which case America would have continued operating under the Articles of Confederation. Our American ancestors didn't want a government of omnipotent powers. They wanted a government of few, limited, enumerated powers.
Among the most omnipotent powers a government can wield is the power of government officials to assassinate people. Our American ancestors definitely did not want that type of government. That is why the power to assassinate is not among the enumerated powers of government in the Constitution.