Facts/Syllabus:
It is a federal crime to “knowingly provid[e] material support or resources to a foreign terrorist organization.” 18 U. S. C. §2339B(a)(1). The authority to designate an entity a “foreign terrorist organization” rests with the Secretary of State, and is subject to judicial review. Among the entities the Secretary of State has designated “foreign terrorist organization[s]” are the Partiya Karkeran Kurdistan (PKK) and the Liberation Tigers of Tamil Eelam (LTTE), which aim to establish independent states for, respectively, Kurds in Turkey and Tamils in Sri Lanka. Although both groups engage in political and humanitarian activities, each has also committed numerous terrorist attacks, some of which have harmed American citizens. Claiming they wish to support those groups’ lawful, nonviolent activities, two U. S. citizens and six domestic organizations (hereinafter plaintiffs) initiated this constitutional challenge to the material-support statute. Plaintiffs challenge §2339B’s prohibition on providing four types of material support—“training,” “expert advice or assistance,” “service,” and “personnel”—asserting violations of the Fifth Amendment’s Due Process Clause on the ground that the statutory terms are impermissibly vague, and violations of their First Amendment rights to freedom of speech and association.