Obama can only stop the pipeline crossing the border from Canada. If they want to build it from ND to the Gulf refineries he couldn't do anything about it.
Of course he could. It's interstate, so it wouldn't even be at all difficult.
But they should be building refineries in North Dakota,
Ha ha, build a refinery? In the US? With the EPA and every environmental group in the world standing in the way?
Anyway, you build a refinery and now you have to move the refined product, which means instead of moving one product, you have to move several. Could make a lot more sense to ship one product to where the shipping is easier.