“If he didn’t mean it, he shouldn’t have said it.” Referring to President Obama, environmental activist Bill McKibben was saying this a lot during the sit-ins he recently led outside the White House to urge Obama to block a climate-killing tar sands pipeline to run from Canada to the Gulf of Mexico. Two weeks of protest resulted in 1,253 arrests, making it one of the largest acts of civil disobedience by US environmentalists in decades. It concluded September 3, one day after Obama made one of the most fateful—and shameful—decisions of his presidency: ordering the EPA to delay new regulations on ozone emissions because the rules pose undue “burdens” on corporate polluters.

McKibben was urging Obama to live up to his 2008 pledge that in his presidency the rise of the oceans would begin to slow and the planet begin to heal. Of course, some might claim the standard to which McKibben is holding Obama is politically naïve. Candidates for president routinely make promises they don’t keep. But voters aren’t stupid. What matters is why a candidate breaks a promise: is it because he won’t deliver, or he can’t? If a president falls short because of circumstances beyond his control or insurmountable opposition, voters can understand and even forgive—if the president puts up a fight. But if a president fails because of mistakes or weakness—if he is not seen as a strong leader—it leaves voters confused, demoralized and open to alternatives.

Obama has thirteen months to persuade voters that they should blame not him but the GOP for his presidency’s shortcomings. He has much less time to convince the thousands of activists nationwide—who do the grunt work of getting out the vote—that he’s worth their sweat and sacrifices one more time.

It’s no secret that Obama is far from closing either deal, and the tar sands pipeline and ozone regulations demonstrate why. Yes, the president has done some good things on the environment; the fuel efficiency standards he pushed through this year, for example, will significantly lower air pollution and greenhouse gas emissions. But he has done bad things as well, including opening vast tracts of the West to coal mining and providing much more funding to nuclear and fossil fuel than to green alternatives.

Obama’s ozone decision, however, has provoked particular outrage, for four reasons. First, by ordering the EPA to delay the promised ozone regulations, the president repudiated science; the independent panel of experts advising the EPA were unanimous in recommending the tougher regulations, which would reduce incidence of child asthma and avoid 12,000 deaths a year. Second, Obama’s order was possibly illegal. The Clean Air Act expressly forbids the government to consider the economic impacts of its regulations; public health is the sole criterion (a stipulation upheld in 2001 by the Supreme Court, with none other than archconservative Justice Antonin Scalia writing the opinion). EPA administrator Lisa Jackson, who has described the existing regulations as “not legally defensible,” has now been undercut by her boss, raising questions about whether she—the administration’s strongest environmental voice—will resign. Third, in making his announcement, Obama channeled the antigovernment mantra of the Chamber of Commerce, citing “the importance of reducing regulatory…uncertainty,” thus buttressing the discredited argument that regulation costs jobs. Fourth, Obama blatantly double-crossed environmentalists, who were suing the EPA over these regulations when Obama took office. His aides persuaded them to drop the suit because Obama’s EPA would soon strengthen the regulations.

Overriding the EPA in this manner sets an ominous precedent for the tar sands decision, which Obama is scheduled to make by year’s end. Bear in mind, as the president likes to say, that both decisions are his alone; he can’t blame Congress for tying his hands. The EPA has twice lambasted reports by the State Department that absurdly claim that the Keystone XL pipeline—projected to transport the dirtiest fossil fuel on earth across 1,700 miles of North America, including the crucial Ogallala aquifer—would have “no significant environmental impact.” Citing the EPA’s estimate that the tar sands in Alberta, if burned, would emit 82 percent more greenhouse gases than conventional fossil fuels, McKibben has called the pipeline “a fuse to the second-largest pool of carbon on the planet,” behind Saudi Arabia. The claim that the tar sands will reduce US dependence on petro-dictators is just as dubious. One of the refineries the pipeline will supply in Texas is half-owned by Saudi Arabia’s state oil company.

Mainstream voices tell progressives unhappy with Obama to grow up: your whining threatens to elect a Republican in 2012, who would be much worse. But they are the ones who aren’t savvy. Fear of the dark side will cause most of the Democratic base to give Obama their votes, but it will not be enough to persuade them to give up their evenings and weekends to get out the vote for him, to sway independent and undecided voters. It’s a normal reaction. If Obama approves the pipeline, explains Courtney Hight, his Florida youth-vote director in 2008 who was arrested in the protest outside the White House, “it is just human nature that the resulting disappointment will sap the enthusiasm that drove us to work so hard last time.”

Obama still has time to bring his message into line with the stirring vision he conveyed in 2008. Perhaps, however, he thinks he can win without a strongly motivated base, relying instead on the powers of incumbency, not least the enormous amounts of money he is raising. If he chooses that course and it fails, spare us any prattle about unsophisticated progressives being at fault. A defeated Obama will have no one to blame but himself.