Once again, the Obama administration has pushed back a final decision on the controversial Keystone XL pipeline. The delay could push the final determination until after the November midterm elections.

In announcing the delay, the State Department cited a Nebraska Supreme Court case that could affect the route of the pipeline, as well as additional time needed to review 2.5 million public comments on the project. The Nebraska case may not be decided until next year.

“The agency consultation process is not starting over,” the State Department said in a statement. “The process is ongoing, and the department and relevant agencies are actively continuing their work in assessing the permit application.”

The delay relieves pressure on President Obama to make a decision anytime soon. If he approved the pipeline, he would anger environmentalists, an active part of the Democratic base. A decision against it could jeopardize vulnerable Democrats who favor its construction, such as Sen. Mary Landrieu of Louisiana. Democrats are fighting to maintain control of the Senate in the November midterms.

At issue is whether the $7 billion, 1,179-mile pipeline extension, which links Canadian tar sands with refineries in Texas, is in the national interest. The pipeline requires State Department study and approval because it crosses the US-Canada border. That evaluation has been under way for five years.

Environmentalists say the extraction process of tar sands is energy-intensive and would contribute to climate change. They also raise concerns about spills. Proponents of the pipeline say it is a job-creator that would help wean the United States from oil that comes from unstable parts of the world.

In January, the State Department issued a report saying it had no major environmental objections to the pipeline but stopped short of recommending final approval.

Friday’s news drew swift reaction from various corridors. Chief executive Russ Girling of TransCanada, the Canadian pipeline operator, said he was “extremely disappointed and frustrated,” according to Reuters. US-Canada relations have been strained over the long decisionmaking process.

"Today's decision by the administration amounts to nothing short of an indefinite delay of the Keystone pipeline," Senator Landrieu said. "This decision is irresponsible, unnecessary, and unacceptable."

Reince Priebus, chairman of the Republican National Committee, framed the decision as political.

"The Obama administration has once again taken the side of the far left, moneyed interests of their party instead of American workers and families,” Mr. Priebus said. “President Obama's stall tactics will continue to cost American jobs – including the vulnerable Senate Democrats that refuse to campaign with him.”

Priebus invoked the name of Tom Steyer, a billionaire environmentalist who has pledged to spend up to $100 million helping candidates who support climate change legislation.

“Tom Steyer: 1; American jobs: 0,” Priebus said in his statement.

Some environmentalists, such as the group 350.org, expressed disappointment that the State Department didn’t definitively reject the project. Others, such as the Natural Resources Defense Council (NRDC), called the delay prudent.

“It is already clear that the Keystone XL tar sands pipeline fails the climate test and will damage our climate, our lands, and our waters,” said Susan Casey-Lefkowitz, director of the International Program at the NRDC.

“Getting this decision right includes being able to evaluate the yet-to-be determined route through Nebraska and continuing to listen to the many voices that have raised concerns about Keystone XL.”

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Last week, the White House rejected a letter from 11 Senate Democrats, many of them in tough reelection battles, urging Mr. Obama to make a decision on the pipeline by May 31.

On Wednesday, Jimmy Carter because the first American ex-president to come out against the pipeline, joining a group of Nobel laureates in opposition. Two years ago, former President George W. Bush called the project a “no-brainer.” Ex-President Bill Clinton also came out in favor in 2012, noting that the pipeline’s redrawn route avoided Nebraska’s ecologically sensitive Sand Hills region.