to the existence of its power to hear the case" without presuming the truthfulness of the plaintiff's allegations. Makro Capital of America, Inc. I. UBS AG, 543 F.3d 1254, 1258 (11th Cir. 2008) (citations omitted); see also, e.g., McMaster. United States, 177 F.3d 936, 940 (11th Cir. 1999) ("[W]e deter