Actually Mr Heisbourg, it has to do with the fact that UNESCO was and is being abused by its Muslim member states and their supporters in order to promote an anti-Semitic agenda, and that's simply unacceptable to the US Presidency (whoever the incumbent) and to all decent people. In this case, its simpler just to read the lines, rather than between them.  Pity though that UNESCO has to suffer for the outrages of certain members.