Canada’s record on technical innovation, except in resource extraction, is notoriously poor. Capital and talent flow to the tar sands, while investments in manufacturing productivity and high technology elsewhere languish.

But more alarming is the way the tar sands industry is undermining Canadian democracy. By suggesting that anyone who questions the industry is unpatriotic, tar sands interest groups have made the industry the third rail of Canadian politics.

The current Conservative government holds a large majority of seats in Parliament but was elected in 2011 with only 40 percent of the vote, because three other parties split the center and left vote. The Conservative base is Alberta, the province from which Prime Minister Stephen Harper and many of his allies hail. As a result, Alberta has extraordinary clout in federal politics, and tar sands influence reaches deep into the federal cabinet.

Both the cabinet and the Conservative parliamentary caucus are heavily populated by politicians who deny mainstream climate science. The Conservatives have slashed financing for climate science, closed facilities that do research on climate change, told federal government climate scientists not to speak publicly about their work without approval and tried, unsuccessfully, to portray the tar sands industry as environmentally benign.

The federal minister of natural resources, Joe Oliver, has attacked “environmental and other radical groups” working to stop tar sands exports. He has focused particular ire on groups getting money from outside Canada, implying that they’re acting as a fifth column for left-wing foreign interests. At a time of widespread federal budget cuts, the Conservatives have given Canada’s tax agency extra resources to audit registered charities. It’s widely assumed that environmental groups opposing the tar sands are a main target.

This coercive climate prevents Canadians from having an open conversation about the tar sands. Instead, our nation behaves like a gambler deep in the hole, repeatedly doubling down on our commitment to the industry.

President Obama rejected the pipeline last year but now must decide whether to approve a new proposal from TransCanada, the pipeline company. Saying no won’t stop tar sands development by itself, because producers are busy looking for other export routes — west across the Rockies to the Pacific Coast, east to Quebec, or south by rail to the United States. Each alternative faces political, technical or economic challenges as opponents fight to make the industry unviable.

Mr. Obama must do what’s best for America. But stopping Keystone XL would be a major step toward stopping large-scale environmental destruction, the distortion of Canada’s economy and the erosion of its democracy.