Assuming the truth of one or more premises is not a fallacy; it is just what one does in any argument. If your argument is valid (i.e., if the premises are true

Assuming the truth of one or more premises is not a fallacy; it is just what one does in any argument. If your argument is valid (i.e., if the premises are true, then the conclusion must follow), it can still be shown to be unsound by showing that one or more of its premises are, in fact, false. And while we often hold that extraordinary claims require extraordinary evidence, it is not a formal fallacy to state an extraordinary premise without adequate justification. Whether you can get anyone to accept it is another matter. It is generally easier if you can find someone who likes your conclusion, which is how most political debate works.