President Donald Trump’s phase-one trade deal with China offers the promise of more overseas sales for American farmers, but the impact of the agreement remains unclear.

Trump has promoted a commitment by China to purchase $40 billion to $50 billion annually in farm products for the next two years. That compares with $24 billion in agricultural and related products that China imported from the U.S. in 2017, before the trade war began.

In an agreement signed Wednesday at the White House, China committed to importing at least $12.5 billion more agricultural goods this year than in 2017, rising to $19.5 billion next year. The Asian nation will also “strive” to purchase an additional $5 billion a year in farm products. That could get total purchases next year toward the $50 billion mark.

But doubts have surfaced on whether China will meet that target, particularly since the two governments have said they will keep secret the purchase benchmarks for individual commodities. China hasn’t committed to specific tariff reductions under the agreement and may simple step up waivers to enable increased purchases of U.S. goods.

“Just count me as skeptical,” said Roger Johnson, president of the National Farmers Union, the nation’s second-largest general farm organization, who spoke ahead of the signing ceremony. “We’ve been down this road so many times before.”