WASHINGTON — President Barack Obama’s decision to block the Keystone XL oil pipeline has exposed an endlessly polarized Washington, and likely hardened its divides.

Obama is now being praised to the skies by environmentalists and most Democrats, and denounced in apocalyptic terms by Republicans and the business community. And although environmental issues once produced bipartisan agreement in Congress, consensus on action to increase energy production or deal with climate change looks farther away than ever.

“This became a tribal issue of bizarre proportion,” said Jason Grumet, president of the Bipartisan Policy Center.

Grumet said voters support Keystone and infrastructure projects, as well as action on climate change. “And unfortunately rather than recognizing the opportunity to do both, we now have a country that’s essentially doing neither,” he said.

Seven years in the making, Obama’s decision to reject the Keystone pipeline to carry crude oil from Canada to the Texas Gulf Coast was not a foregone conclusion, at least not initially. From one perspective the pipeline is merely an infrastructure project, unlikely to cause major lasting impacts on jobs or the environment, according to government analyses. In 2010, then-Secretary of State Hillary Rodham Clinton said her department was inclined to sign off on it.

But that same year Democrats lost control of the House after infuriating Republicans by forcing through a bill cutting greenhouse gas emissions. Legislative efforts on climate change were declared dead, and environmentalists began shifting their focus onto the executive branch, seizing on Keystone as a place to make their stand.

As environmentalists staged protests and chained themselves to the White House gates, Keystone transformed into a litmus test for both sides. In the Republican view, opponents of the project were backing environmental extremism over jobs. Ask Democrats, and the project meant environmental destruction and a giveaway to the fossil fuels industry in place of sensible action to curb climate change.

Clinton announced her opposition to the project in September as she campaigned for president, and in the wake of that announcement Obama may have had little choice but to follow suit, given the intense pressures he faced. Those pressures would only have intensified heading into international climate talks in Paris later this month.

In the view of some, the debate became unchained from reality, an election-season wedge issue that forced Republicans and Democrats into their corners, each denouncing the other as extreme. Not so long ago legislation like the Endangered Species Act and the Clean Air Act won bipartisan support on Capitol Hill, but in today’s atmosphere such cooperation looks almost unimaginable.