<prompt> Translate the following text to EnglishVisa vya kusafiri vya Marekani vinatakiwa kuwezesha usafiri halali na wakati huo huo kukataa kuingia Marekani kwa watu fulani, ikiwa ni pamoja na magaidi wa uwezekano.  <response>: The visa function attempts to facilitate legitimate travel while at the same time denying entry to the United States of certain individuals, including potential terrorists. 