A Canadian company has sued the US demanding that the US construct the Keystone XL pipeline or pay 15 billion dollars.

The lawsuit is under the original NAFTA treaty, which has an ISDS clause ("I sue democratic states") It is peculiar that this lawsuit is proceeding, given that NAFTA was replaced by a newer treaty which does not have an ISDS clause. The article notes this peculiarity but does not explain how that is possible.