Mexico is irreplaceable as a foreign market that buys billions of dollars of milk, ham, rice, potatoes and corn, so farm groups are alarmed by President Donald Trump’s renewed threats to shut down the southern border.

The U.S.-China trade negotiations return to Washington this week amid signs of progress, while Senate Republicans seek to move forward with a long-stalled package of disaster aid eagerly awaited by a growing list of farmers.

U.S. negotiators head to China this week to resume face-to-face trade talks, and the Senate is expected to consider a long-stalled disaster aid bill amid demands to expand it to include assistance for losses from the Midwest flooding.

The USDA announced Friday that China is making a significant purchase of U.S. corn after years of deteriorating trade, spurring hope that the trade talks between the two countries are producing real progress that could have lasting effects.

President Donald Trump said Wednesday he’s planning on leaving U.S. tariffs on Chinese products in place “for a substantial period of time,” even after some form of deal is reached with China.