The teams start rolling out before daybreak, a rumbling cacophony orchestrated under floodlights and black skies. They fan out, men carrying hardhats walking past trucks on the move, busloads of workers, and trailers carrying four-wheel-drive carts and heavy machinery. About 700 workers building TransCanada’s Keystone XL pipeline in Texas move out from a Mount Pleasant lot every morning in a mobilization fit for a war zone. The size of the effort, for just one segment of Keystone XL, is part of TransCanada’s sophisticated, 4,000-person operation to dig through nearly 500 miles of land and install a 36-inch diameter oil pipeline...