Obama Backs Plan to Build Southern Leg of Keystone XL

Barack Obama helped put the Keystone XL tar sands pipeline back on track on Monday, endorsing construction on a key southern portion of the controversial project.

The White House support for construction of a southern portion of the pipeline, running from Cushing, Oklahoma to Port Arthur, Texas, essentially unravels its rejection of the entire project just one month ago.

The move was seen by environmental campaigners as a betrayal. The Sierra Club described the revival of the pipeline project as a "dirty trick."

But the maneuver could insulate Obama in an election year from what was emerging as a key line in Republican attacks: that he had sided with environmental campaigners against America's energy security and jobs.

TransCanada, the Canadian firm behind the pipeline, announced on Monday that it was pushing ahead with construction on a southern portion of the pipeline, running from Cushing to Port Arthur.