The Keystone XL pipeline could bolster U.S.-Canadian ties, but uproar over oil sands has become a source of friction, writes Steven Mufson for the Washington Post.

Loring, Mont. — At the remote border crossing north of here, two stern U.S. border guards emerged from their spanking new post to check passports. There wasn't another person or car in sight. An uninterrupted sea of prairie stretched in every direction.

On the Canadian side, the nearest town is Val Marie, the entrance to Grasslands National Park and home to 137 people. On the U.S. side, it's Loring, population nine — not counting the dog called mayor.