NEW : The Justice Departments ' Office of Legal Affairs provides the president with a preliminary legal opinion . Trump 's plan to invade Syria is not legal under international law , they say . Congressional approval would lend it some legitimacy , an administration official says . That 's in part because Syria is n't among the 188 countries , including the United States , that signed the Chemical Weapons Convention , the treaty that prohibits the production and use of such weapons . Others briefed on the administration 's plan say it is too broad .
NEW : The Justice Departments ' Office of Legal Affairs provides the president with a preliminary legal opinion . Trump 's plan to invade Syria is not legal under international law , they say . Congressional approval would lend it some legitimacy , an administration official says . Others briefed on the administration 's plan say it is too broad .