TransCanada last week defended its environmental legacy against critics who contend the project would lead to higher greenhouse gas emissions. President Obama said the project would be weighed against its carbon footprint. TransCanada said the emissions would be negligible.
TransCanada needs a presidential permit to build a cross-border section of the pipeline from Alberta. A domestic leg from Oklahoma is under construction.
Girling told Bloomberg News last week the project was becoming a scapegoat for critics of oil sands, the type of crude oil designated for the pipeline.
"Denial of this pipeline is not in any way rational," he said in a interview published Friday. "At best, it's symbolic."
Supporters of the pipeline say it would ensure North American energy security while providing a source of economic stimulus.
The State Department is vetting public comments made on a draft environmental assessment, which found emissions would be problematic with or without the pipeline.
"Keystone is not the driver of whether Canadian oil sands will be produced," Girling said.
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