A third-term U.S. senator made this vigorous case last week for President Barack Obama to finally approve completion of the Keystone XL pipeline: “It’s just a no-brainer. Canada is going to export this oil. It’s either going to come to the U.S. or it’s going to go to Russia or China.”

No, that wasn’t a Republican lawmaker still dishing up sour grapes over the GOP’s reversals in last month’s election.

That was Democrat Mary Landrieu, the senior senator from Louisiana, telling The Associated Press about her continued frustration with the administration’s opposition to the Keystone plan.

Three weeks ago, she joined eight fellow Democrats and nine Republicans in signing a letter urging the president to allow construction on the northern leg of the Keystone pipeline.

President Obama caught her — and lots of other people — by surprise early this year when he rejected TransCanada’s long-standing permit request to build the pipeline over the U.S. border. The $7 billion project is designed to move oil from Canada’s tar sands nearly 1,700 miles to the Gulf of Mexico.

The White House’s stance at the time was widely perceived as an attempt to maintain President Obama’s widespread support from the environmental community during his re-election bid.

However, despite some overwrought protestors’ overstated concerns about water contamination, this pipeline — and there are plenty of others already in service — doesn’t look like an environmental disaster waiting to happen. Most of the resistance to it apparently is less about water quality than what the pipeline would safely deliver — oil.

Many environmentalists remain disappointed in the Obama administration’s failure to address climate change — and by America’s long-term dependence on fossil fuel.

Danielle Droitsch, a senior attorney with the National Resources Defense Council, told the AP: “The broader climate movement is absolutely looking at this administration’s Keystone XL decision as a really significant decision to signal that dirty fuels are not acceptable in the U.S.”

Yet recognizing the need to reduce carbon emissions shouldn’t blind Americans to energy realities.

Nor should we neglect this opportunity for mutually beneficial trade with our neighbor to the north.

Canadian Prime Minister Stephen Harper offered this heated response after President Obama nixed the pipeline completion: “I think what’s happened around the Keystone is a wake-up call, the degree to which we are dependent or possibly held hostage to decisions in the United States, and especially decisions that may be made for very bad political reasons.”

Washington Post financial columnist Robert Samuelson was even more riled up, branding the White House’s derailing of the pipeline “an act of national insanity.”

But with another permit application coming up for review, the White House now can — and should — correct that mistake.

It simply makes no economic, energy or environmental sense to block a pipeline that would safely bring reasonably priced oil to U.S. refineries.

And as Sen. Landrieu put it last week: “Even Democrats that aren’t really excited about oil and gas development generally can figure that out.”