Alberta tar sands oil and North Dakota light shale oil flows into the same markets, have access to the same refineries, and rely on the same pipelines and railroads to get them to the same customers. So it was never terribly plausible that Keystone would be good for the U.S. -- it was designed to make Canadian oil more competitive in global markets.
Tar-sands supporters in Congress will find it hard to tune out the fossil-fuel interests that want to see Canada's oil sands mined to the utmost. After all, the biggest foreign lease holder in Canada's oil sands is none other than the Koch brothers. But we'll cross that bridge when we come to it. For now it's up to President Obama to do the right thing.