In an otherwise excellent critique of Donald Trump's trade policy, Mercatus economist Veronique de Rugy writes: Worst of all, the deal would actually reinforce these Chinese behaviors. For instance, the deal in question would require that China use its state-owned enterprises to buy $40 billion to $50 billion worth of American agricultural products annually—instead of the roughly $20 billion it bought previously. That's no victory. That's a concession China already agreed to more than two years ago. And that's...