WASHINGTON — WHEN I was elected to Congress in 2002, George W. Bush was president and big business wrote environmental policy. We all remember Vice President Dick Cheney’s energy task force — a who’s who of mining and oil interests — and the administration’s constant questioning of climate science.

President Obama won the White House by running as an agent of change: change from Mr. Bush’s way of doing business with business, and change from Washington’s habitual corporate favoritism.

I was an enthusiastic supporter of the president then and I still am — I consider his environmental record a tremendous improvement over his predecessor’s.

But that record is still being written, and it is heading in the wrong direction. If the president approves the Keystone XL pipeline on the basis of the lobbying and bad science that has been offered to support it, much of his good work will be undone and a business-as-usual atmosphere will settle back on Washington like a heavy cloud. It would be a bad end to what could still be a very strong environmental legacy.

The pipeline has drawn more critical attention than its corporate sponsors seemed to expect, and it is important to understand why that happened. Keystone is a bad deal for the American taxpayer on the merits, but that’s not the only reason. More important, environmentalists have decided that enough is enough.

We saw plenty of important decisions made during the Bush era in the name of “streamlining,” “cutting red tape” or “using sound science” — that is, science funded by an industry that wanted less oversight. In November 2008, millions of Americans breathed a sigh of relief and told themselves those days were over. Keystone has rallied the entire environmental community because it is a visible and sometimes painful reminder of the way things were done under Mr. Bush.

The administration’s approach to the pipeline is a throwback to the time when endangered species were defenseless in the face of corporate moneymaking. It is a reminder that even though our environmental laws use science, not profits, as the basis of our environmental decisions, any company with bottomless pockets used to be able to game the system and get away with it.

That’s why Keystone is about more than one pipeline. It is about establishing once and for all whether we have moved on from the disastrous Bush-Cheney view of environmental policy. President Obama’s own Environmental Protection Agency has said in no uncertain terms that the pipeline will contribute significantly to greenhouse gas emissions. That should be the end of the conversation. The fact that it isn’t — that we’re left hanging and hoping — is more than disappointing. It is a very troubling sign for the future.

As the news media has reported widely, the contractor chosen by the State Department to assess the pipeline’s environmental impacts violated federal conflict-of-interest rules to get the job, and nothing has been done about it. That company, Environmental Resources Management, did work for TransCanada, Keystone’s parent company, in the recent past and told the State Department the exact opposite on disclosure forms that anyone in the world can now read for herself. A report on Wednesday from the State Department inspector general, which many outlets covered as though it exonerated the department and E.R.M. of wrongdoing, is actually an important example of the problem. The I.G. only looked at whether the department followed its existing process for choosing a

contractor. It should have looked at whether that process produces reliable outcomes.

If E.R.M.’s decision that Keystone does not pose any environmental risks is allowed to stand, it will not just move Keystone closer to an unjustified approval; it will re-establish the Bush-era habit of tipping the scales in favor of corporations that want special treatment.

Anyone who believes it is unfair to make Keystone a litmus test of Mr. Obama’s environmental record is looking at recent history backward. The environmental community did not make any of this happen. If E.R.M. had come clean, we wouldn’t be in this position. But it didn’t, and we are. At some point we have to decide that it won’t happen again.

Depending on the outcome, I worry that the American public won’t just lose faith in Keystone. It will lose faith in the government’s ability to fund, carry out, understand and implement scientifically based environmental policy. President Obama doesn’t want that to be his legacy. Neither do I. And I am hardly alone.

Representative Rau?l M. Grijalva, Democrat of Arizona, is co­chairman of the Congressional Progressive Caucus.