If you and and every other Freeper posting posting blather about how the job has to be offered to, and turned down, by the Speaker, or President pro tempore, before the Secretary of State gets a chance to act as President, and/or that the Secretary of State has to take the Presidential oath before acting as President, would bother to read the XXth Amendment, and Presidential Succession Act, you would see that the power to act as President devolves to the Secretary of State automatically, instantly. The Amendment and law were crafted so that if the Soviets nuked the President and Vice President, the remaining US Government would have an official who was acting President, without any delay for consultation, resignation, oath taking, and the like. In the event of a prolonged interval without a duly elected President, who has qualified by taking the oath, the Speaker, or President pro tempore, may resign, take the Presidential oath, and become acting President ahead of the Secretary of State, but until they do the Secretary of State is also acting President.
Your problem is that there is a duly elected president who would take office sans oath. Congress has already certified his victory so as soon as Hussein is removed by statute Trump is instantaneously president.
There is no issue here.