A battle is raging over Israel's declaration that six Palestinian non-governmental organizations (NGO) are fronts for the Popular Front for the Liberation of Palestine (PFLP), a U.S.-designated terrorist group. Several American NGOs are lashing out at Israel for the move. But they are skating on thin ice. Some of them have worked closely with the six NGOs in question. And if Israel's accusations prove to be true, they could find themselves in hot water. The PFLP has been listed on the State Department's list of Foreign Terrorist Organizations since 1997. The group has actually been engaged in terrorist activity since...