We don't need laws to make it illegal for American citizens to give money to terrorist organizations. Congress simply needs to treat the terrorists as foreign paramilitary organizations, and declare war on them. It is illegal for Americans to assist enemies of the United States. Some terrorists claim to be soldiers whom we should treat as prisoners of war. Let's do exactly that.
International law requires combatants to wear uniforms.
Terrorists disguise themselves as civilians, which is a capital military crime. If they attack the United States while wearing uniforms, I agree that we should treat any survivors as POW's. The United States should always seek respect, and not hate or fear. If, however, terrorists take this for weakness and irresolution, they must learn the full meaning of oderint, dum metuant . The lightning bolts are aspects of the god Jupiter.