His greens are certainly in evidence, camped in ever greater numbers in front of the White House to protest the proposed Keystone XL pipeline that will move oil from Canada to the Gulf of Mexico. The pipeline officially needs State Department approval, though this week Mr. Obama further elevated the controversy by announcing that he would be making the final call.

Which gets us to his blues, or rather the 20,000 blue-collar construction jobs that would come with the pipeline, and the further 118,000 spin-off jobs. The unions—from the Teamsters, to the Plumbers and Pipefitters, to the Laborers—are out in force pushing for this giant job creator. “We can’t wait to get America building again,” blares a union-sponsored website in support of Keystone, poking at the president’s latest political rhetoric.

Keystone is more than just the administration’s latest headache. It’s the clear culmination of an Obama governing philosophy that has consistently put green priorities ahead of blue-collar workers, and that is now one of the biggest threats to his re-election.

This isn’t a constituency Mr. Obama should ever have dared to slight. Working-class white males were the Hillary Clinton bloc in 2008 and helped her trounce him in key states such as Pennsylvania and Ohio. Mr. Obama would go on in the general election to lock up the college-educated, the affluent, the women, the minorities, the first-time voters—you name it. He lost the white working class by 18 points.

Rather than court this constituency, Mr. Obama has spent three years waging war on them. Under the sway of (former) green czar Carol Browner, Environmental Protection Agency Director Lisa Jackson and the environmental lobby, the Obama administration has done more to kill working-class industries than any modern predecessor.

Associated PressDemonstrators for and against the Keystone XL pipeline in Lincoln, Neb.

The EPA has labored over an ozone rule (estimated job losses: 7.3 million), power plant rules (1.4 million), a boiler rule (789,000), a coal-ash rule (316,00), a cement rule (23,000), and greenhouse gas rules (even Joe Biden can’t count that high). The administration blew up Louisiana’s offshore deepwater drilling industry, insisted Detroit make cars nobody wants to buy and, just to stay consistent, is moving to clamp down on the country’s one booming industry: natural gas.

Those going the way of the dodo are utility workers, pipefitters, construction guys, coal miners, factory workers, truck drivers, electrical workers and machinists. Many of these are union Democrats who don’t care if their union bosses are publicly sticking with the president. They are pessimistic about the future and increasingly angry over the president’s attack on their work.

A Pew poll this year found an astonishing 43% of the white working class didn’t believe they’d be better off in 10 years—the most negative views of any group polled, by far. It helps explain why, in the 2010 election, the white working class surged to give the GOP a record 63% of their vote, 30 points more than for Democrats. It’s why a poll out of the Center for Opinion Research at Franklin & Marshall College in Pennsylvania just found that 59% of union households now say they want someone in the White House other than Barack Obama.

Despite the media obsession with America’s changing demographics, blue-collar, white workers still make up 40% of the electorate, even more in states Mr. Obama needs. The latest 2012 census data suggest that white working-class voters could make up some 55% of the Ohio, Pennsylvania and Michigan votes.

This explains the White House’s recent decision to delay or scale back some EPA regs, including on greenhouse gases and ozone. A red-faced Mrs. Jackson has issued all manner of excuses. But the reality is the rule changes were a direct give-back to the blue-collar unions, which have been publicly protesting the regulations and privately warning the administration about electoral death. The White House had also been getting an earful from vulnerable congressional Democrats, who threatened to start voting with Republicans against these job-killers if the White House didn’t take them off the table.

More telling is that the White House is moving in a way that suggests even it knows these gestures come too late. Mr. Obama is throwing his campaign attention at Southern and Rocky Mountain states he won in 2008 (North Carolina, Virginia, Nevada, Colorado), looking for a way to 270 that goes around the Rust Belt.

This might also help explain Mr. Obama’s continued dithering on Keystone XL. Most presidents would eat dog food for the chance to generate a job bonanza and billions in investment with a project his own State Department says poses no environmental threat. But the green lobby hates it, and that green lobby is a staple of the liberal, educated, affluent base, and that’s the group the Obama team is ever more convinced it’s going to need in 2012.

And so we have a president who is seriously considering tanking thousands of union jobs, in a 9% unemployment economy, and while on a jobs tour. If that sounds crazy, well . . .

Write to kim@wsj.com