UPDATE 2-Trump targets China cooking oil trade – but sales were already tanking

* U.S. cooking oil imports from China dropped 65% this year * Trump's comments have minimal impact, traders say * China shifts soybean purchases to Brazil, Argentina (Recasts; adds comments from traders and analysts in paragraphs 5-7 and 9, context throughout) WASHINGTON/BEIJING, Oct 15 (Reuters) – U.S. President Donald Trump said he was considering terminating some trade ties with China, singling out cooking oil even though traders and analysts said such shipments have already spent the past year plummeting. "I believe that China purposefully not buying our Soybeans, and causing difficulty for our Soybean Farmers, is an Economically Hostile Act. We are considering terminating business with China having to do with Cooking Oil, and other elements of Trade, as retribution," Trump wrote on so