On Feb. 17, more than 40,000 people rallied in Washington, D.C., to convince the president to reject the Keystone XL, a proposed 875-mile pipeline running from the Canadian border into Nebraska and slated to transport oil from tar sands (which is 17 percent more greenhouse-gas intensive than standard crude oil). The crowds outside the White House provided overwhelming proof that opposing Keystone has mobilized a new and powerful grassroots constituency.

But in the U.S. Senate, the mood was different. In a non-binding vote, 62 senators — including 17 pro-Keystone Democrats — voted to approve the pipeline. Just 37 senators voted against it. In fact, the amendment was co-sponsored by four Democrats, including Max Baucus of Montana and Heidi Heitkamp of North Dakota.

So are activists’ efforts all in vain? What will happen to the environmental movement if President Obama ultimately lets Keystone go forward?

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And more broadly: What does this say about the best strategy for fighting climate change? Does compromise, horse-trading, and winning industry allies ultimately work best — or do you have to push the limits of the possible? You’re invited to the next Climate Desk Live event — hosted by myself — for a debate and discussion between some of the leading voices on this issue:

May Boeve, executive director and co-founder, 350.org.

David Roberts, Grist writer, who has been covering Keystone regularly and recently wrote about the “Virtues of Being Unreasonable on Keystone.”

Michael Levi, director of the program on Energy Security and Climate Change at the Council on Foreign Relations, and author of the new book The Power Surge: Energy, Opportunity, and the Battle For America’s Future, where he writes that combating climate change will require “doing deals [with those] who want to expand production of oil and gas.”

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Michael Grunwald, senior national correspondent for Time magazine, author of The New New Deal: The Hidden Story of Change in the Obama Era, who recently declared that on Keystone, “I’m with the Tree Huggers!

Join us for a Climate Desk Live event focused on the Keystone XL: Thursday, April 18, 2013, 6:30 p.m. at the University of California Washington Center, 1608 Rhode Island Ave NW, Washington, D.C. 20036. To attend, please RSVP to cdl@climatedesk.org.

This story was produced by Mother Jones as part of the Climate Desk collaboration.