Each morning for the past two weeks, scores of respectable-looking protestors ushered themselves into single file lines, walked determinedly through Washington’s Lafayette Park, sat down on the sidewalk in front of the White House, arranged themselves in rows as if for a class photo, and waited patiently to be arrested (the violation: blocking pedestrian traffic). As of Friday, the penultimate day of scheduled protests, the total arrest count stood at 1,009—among those booked were former members of Obama's campaign and White House staff.

The specific object of their ire is the 1,700 mile oil pipeline called Keystone XL, which is scheduled to be built from the vast tar sands of Alberta, Canada all the way to refineries in Texas. But the activists don’t hesitate to say whom they would hold responsible for its construction: President Obama himself.

And there’s merit to the charge. With respect to his efforts to enact health-care reform, financial regulation and strike a debt deal, Obama has caught plenty of unfair flak from the left for not “going far enough.” The nagging problem with this line of criticism is it often ignores political realities—say, for instance, the separation of powers. But the decision to allow the construction of Keystone XL—and to permit its unusually noxious environmental repercussions—is in the president’s hands, as a matter of foreign relations. On August 26, the State Department, to whom the decision is officially delegated, indicated early approval for the project with a favorable "Final Environmental Impact Statement." When the eventual determination is made, sometime after Thanksgiving, it can't plausibly be blamed on partisan politics. In that way, the protesters aren’t just objecting to the pipeline—they’re expressing their belief that the President has misrepresented his own commitment to environmentalism.

Protest leader Bill McKibben (also a TNR contributor) and his small army of activists—who together have mounted what they call the largest show of environmentalist civil disobedience in the nation’s history—have a number of objections to the pipeline. Keystone XL would facilitate the use of a heavy Canadian crude oil called bitumen, which not only contains more carbon than regular oil, but whose extraction and refinement leaves about two times as large a carbon footprint as conventional drilling, and wreaks havoc on the local habitat. A July 2011 study by the Canadian government estimated that bitumen oil production alone would lead to a 30 percent rise in the country's carbon emissions by 2020. The pipeline, which would traverse one of the Great Plains’ central water supplies, also poses an enormous spillage risk—the original Keystone pipeline, built by the same Canadian company in charge of XL, has reportedly leaked 12 times since it opened last summer.

As far as the protesters are concerned, this summer has given plenty of reason to be skeptical of the president’s good faith, his strengthened fuel efficiency standards notwithstanding. In June, Obama reneged on his promise to install solar panels on the White House roof. On Friday, he killed a long-anticipated plan to curb smog emissions. Now the administration may let the prospect of the pipeline’s job-creating potential outweigh its demerits. If Obama green-lights the project, which environmental activists are trying to make the defining issue between now and the 2012 election, he’ll likely antagonize a significant portion of his grassroots support, which is slowly, albeit politely, losing patience with his recent ambivalence over combating climate change.