WASHINGTON — The Trump administration’s second package of aid for U.S. farmers hit by the trade war with China is expected to total $15 billion to $20 billion and involve direct payments, the agriculture secretary said Wednesday.The U.S. Department of Agriculture still is finalizing the plan, which likely will prioritize hog and soybean farmers, the products most affected by the trade dispute between China and the United States, Agriculture Secretary Sonny Perdue and industry sources briefed on the plan said.The world’s two largest economies have been embroiled in a 10-month trade war that has cost billions, roiled global supply chains and rattled financial markets.