Environmental groups and some top Democratic donors oppose the pipeline, saying it would carry "dirty oil" that contributes to global warming. They also worry about possible spills.
Tom Steyer, a billionaire environmentalist, has vowed to spend $100 million —$50 million of his own money and $50 million from other donors — to make climate change a top-tier issue in the 2014 elections. Opposition to Keystone XL is a significant part of that effort.
At least one environmental group said Thursday it would look to hold Senate Democrats "accountable" if the pipeline is approved. The group, 350 Action, has staged protests across the country at events where Obama was speaking and could extend that to Democratic campaign events in states where lawmakers have backed the pipeline.
"We will definitely be out there protesting," said Jamie Henn, a spokesman for the group, which is associated with activist Bill McKibben.
Sens. Heidi Heitkamp of North Dakota, Joe Manchin of West Virginia, Jon Tester of Montana, Claire McCaskill of Missouri and Joe Donnelly of Indiana also signed the letter urging approval of the pipeline.
White House press secretary Jay Carney said Thursday that the review of the pipeline "needs to run its appropriate course without interference from the White House or Congress."
The State Department is reviewing the project "and when there's a decision to be announced, it will be announced," Carney said. The State Department has authority over the project because it crosses a U.S. border.
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