Last Monday night, when environmentalist activists staged 280 candlelight vigils in 49 states to protest the proposed Keystone XL pipeline—in Washington, D.C., demonstrators inflated a giant black tube in front of the White House—many no doubt wondered if their long campaign to halt the project had reached a turning point.

"When I saw the photos coming in from the vigils happening all over the country, I looked at my husband and said, 'We have a real movement here,'" said Jane Klebb, who runs Bold Nebraska, a local group opposing the project.

The previous Friday, the State Department had released its final environmental impact assessment of Keystone XL, which would carry heavy oil from Canada's tar sands across Nebraska and five other states to refineries in Texas. The State Department concluded that, though the tar sands have a somewhat larger carbon footprint than other sources of oil, the pipeline was unlikely to affect the rate at which the oil is extracted—one way or another, it would find its way to market. (See related "Scraping Bottom: The Canadian Oil Boom.")

What is the Keystone XL Pipeline?

That conclusion seemed to satisfy President Obama's criterion for approving the project: that it not "significantly exacerbate" the climate problem.

The State Department report stretched over 11 volumes. The group that has spearheaded opposition to the pipeline, 350.org, released a two-word rebuttal: "Game on." (See related story: "Three Factors Shape Obama Decision on Keystone XL Pipeline.")

Hence the vigils.

Over the past several years 350.org, co-founded by global warming activist and author Bill McKibben, has reenergized the environmental movement with a campaign of grassroots mobilization and civil disobedience inspired by the civil rights and anti-Vietnam War movements of the 1960s and 1970s. Now, as the Obama Administration weighs the decision on whether to grant final approval, the moment seems ripe with promise for environmentalists—yet fraught with peril. Have they picked the right fight?

"We have a lot riding on this," Klebb says. "If after five years of fighting and mobilizing people we can't stop this with the amount of resources we've put forward, then what project can we stop?" (See related interactive map of the route: "Keystone XL: Mapping the Flow of Tar Sands Oil.")

View Images Protesters in Santa Monica, California, on February 3, 2014, urge President Obama to reject the Keystone XL pipeline. Photograph by Laura Kleinhenz, Redux

Clash of the Symbols

In the hopes of rallying the public to the fight against climate change, the activists have made TransCanada's Keystone XL pipeline a symbolic test of President Obama's commitment to reducing greenhouse gases. In the process they've sometimes exaggerated the pipeline's intrinsic importance—labeling it, in McKibben's memorable phrase, a "fuse to the biggest carbon bomb on the planet."

In terms of carbon emissions, if you don't buy the argument that the oil from the tar sands is going to get to market somehow, stopping the Keystone XL would be equivalent, according to the State Department's numbers, to stopping the construction of somewhere between half a coal-fired power plant and half a dozen, at a time when China has been building dozens a year. In other words, the pipeline would exacerbate the climate problem incrementally—and perhaps "significantly," depending on your point of view—but it would not (to quote another slogan) be "game over" for the planet.

Proponents of the project wield exaggerated symbolic arguments of their own—that it would promote "energy independence," for instance, and create jobs. The State Department report found it would create 42,000 temporary construction jobs and 50 permanent jobs.

For President Obama, the dilemma is that it is politically difficult to forbid a commercial enterprise for symbolic reasons. A PEW Research Center poll taken last fall found 65 percent of Americans, including 51 percent of Democrats, support the pipeline.

The effort to block the pipeline is already complicating midterm election politics for Democrats in ways that jeopardize the broader environmental agenda. Four of eight Senate Democrats who have expressed support for the pipeline face difficult reelection campaigns; Democrats could lose control of the Senate, and with it the kind of leverage needed to make gains on a host of other environmental issues.

Amy Myers Jaffe, an expert on global energy policy at the University of California at Davis, cautions that the effort to defeat the pipeline may be misplaced. "The environmental movement has made this a litmus test," she says. "It's always dangerous to draw a line in the sand, because then you're stuck with the line."

She says the pipeline battle has overshadowed other achievements on climate change, such as the Obama Administration's new fuel efficiency standards. "There is demand for oil. It's going to move, and rail is more dangerous—we all just saw a town disappear," she says, alluding to the July explosion of an oil train in Lac-Mégantic in Quebec. "If you want to keep oil in the ground, we have to address what kind of cars we want to drive." (Related: "N.D. Oil Train Fire Spotlights Risks of Transporting Crude").

The focus should be on regulating carbon emissions nationally, Jaffe says, "instead of trying to block infrastructure." Later this year, the Obama Administration has promised to propose regulations limiting the emissions from existing coal-fired power plants—a policy move whose effect on climate would potentially dwarf that of the Keystone XL.

Water, Land, and Grassroots

Carbon emissions are not the only environmental objection to the pipeline. Opposition to it gained a foothold first in Nebraska, where farmers raised concerns that a pipeline leak could seep into the Ogallala Aquifer, which supplies drinking water to the Great Plains and irrigation for a third of the nation's farmlands. Klebb's group joined forces with farmers, and TransCanada was eventually forced to redraw the route around the aquifer and the fragile Sand Hills.

That has not been enough to convince all Nebraskans. "The pipeline has brought together a whole group of new voices, in particular rural voices and voices from the agricultural community," Klebb says. "That is hugely significant. This is not just an East Coast—West Coast environmental issue."

Even in oil-friendly Texas, pipeline opposition bloomed. The pipeline route would cross through Julia Trigg Crawford's farm in Lamar County, 120 miles northeast of Dallas. Crawford is now in the third year of a court fight to prevent TransCanada from taking her land.

"When our little fight started off, it wasn't purely environmental, it was property rights—and it grew," she says. "Now it's Democrats, Republicans, Tea Partiers, Libertarians, white, black, gay, straight, city dwellers, country dwellers. I symbolize someone who is going to stand up against mammoth odds." (See related story: "Keystone XL Pipeline Path Marks New Battle Line in Oklahoma.")

Mainstream environmental groups have since thrown themselves into the battle as well. "When we're able to focus on distinct, concrete projects, we tend to win," Michael Brune, executive director of the Sierra Club, told the New York Times. "And when we tend to focus on more obscure policies or places where we need action from Congress, we tend to stall." If Obama approves the Keystone XL pipeline, Brune said, it will be "the Vietnam of his presidency."

Susan Casey-Lefkowitz, who directs the Natural Resources Defense Council's international program, cautions against overemphasizing the pipeline. "The battle is climate change," she says. "Keystone XL is one piece of that fight, one marker on that path."

But she also dismisses the idea that the Keystone skirmish will backfire against the environmental movement.