The only constitutionaly legal action the American state might invoke against Americans on Gaza bound vessels would be indictments for treason; and that could be only AFTER Congress enacts a Declaration of War against Gaza. So what's the difference between an American mercenary in Afghanistan and an American citizen aboard the Tahrir? Absolutely nada!
Firebomb thrown during demonstration in northern Israeli town of Umm al Fahm (Haaretz)
from the article: Israel Navy intercepts Gaza-bound aid vessels; no injuries reported