What if an ISDS tribunal continually levied fines against a nation-state member for damages caused by a breach of international law?
Would that nation-state eventually feel pressured to change its laws to avoid crippling fines?
Would that nation-state eventually feel pressured to change its laws to avoid crippling fines?
This is not a bug but a feature: the ISDS is designed to ensure that states abide by international law and respect the terms of the free trade agreement they consented to. This is fully in line with the concept of pacta sunt servanda and the relationship between international and municipal law.
Finally, if you are the United States, you can also simply ignore the arbitral tribunal and continue to be in breach of the agreement and international law, because, well, what are they gonna do?