The former North American Free Trade Agreement (NAFTA) contained a chapter on investment that allowed foreign investors to sue governments in international arbitration. The owner of Keystone XL — TC Energy (previously TransCanada) — used NAFTA to launch a US$15 billion lawsuit in 2016 after President Barack Obama cancelled the project. At the time, some legal experts thought the company had a reasonable chance of winning. We will never know, because the case was dropped when President Donald Trump indicated he was willing to let the project proceed. This time may be different if TC Energy...