US President Donald Trump is accusing China of “letting us down” by not promptly buying more US farm products.“They have not been buying the agricultural products from our great Farmers that they said they would,” the president said on Twitter. “Hopefully, they will start soon.”After meeting with Chinese President Xi Jinping late last month, Trump said China had agreed to buy more US agricultural products as part of a ceasefire in the two countries’ trade war.The truce suspended US plans to…