dondon:

Whenever one party unilaterally changes the terms of an agreement, unless there is a provision specifically to the contrary, the agreement has been breached and therefore is unenforceable. Obama through his demands regarding environmental requirements as well as placing not previously existing conditions upon the supply of oil from Canada to the United States, would be abrogating previously existing commercial agreements. On this one, I would play hardball. Of course after confirming my legal footing.

Brian