GWEN IFILL: Now to the political power struggle over legislation to build the Keystone XL pipeline, which landed today on the president's desk and was promptly vetoed.

The president chose to carry out the veto in private, out of the glare of cameras, a sharp contrast to House Speaker John Boehner's decision to stage a very public bill signing at the Capitol only 11 days ago.

SEN. JOHN HOEVEN: Senate Bill 1, as amended, is passed.

GWEN IFILL: The Keystone bill was the first order of business after Republicans claimed majorities in both houses of Congress this year. It's been seven years since the 1,200-mile-long pipeline was first proposed. Parts of it are already under construction, with the ultimate goal of carrying Canada's tar sands oil to refineries along the Gulf Coast, a project many lawmakers say would create needed jobs.

But environmentalists and landowners in some of the states it would travel through argue it would cause more harm than good.

White House Press Secretary Josh Earnest said the president's veto is not about the merits of that argument, but about the review process.

JOSH EARNEST, White House Press Secretary: It just merely says that the benefits and consequences of building that pipeline should be thoroughly evaluated by experts and through this administrative process that has existed for decades and has been used by previous presidents of both parties.

GWEN IFILL: But Republican criticism was swift.

SEN. JOHN BARRASSO, (R) Wyoming: But the president does have his pen. And by choosing to veto this piece of legislation, he is choosing Washington lobbyists and special interests over the needs and desires of the American people.

GWEN IFILL: The next step for the pipeline is unclear. Republicans would have to muster a two-thirds majority in the House and Senate to override the veto.

We get reaction now from Robert Bryce, a senior fellow at the Manhattan Institute, who writes widely on the energy sector, and Jeremy Sions — Symons — pardon me — senior director for climate policy at the Environmental Defense Fund.

Robert Bryce, if this was a question or a debate over jobs vs. the environment, who won today?

ROBERT BRYCE, Manhattan Institute: You know, Gwen, I would say it's a tossup, but I would say that the pipeline, the symbolism over this pipeline has far outstripped its importance in terms of energy security, energy independence, energy imports, et cetera.

Remember, since 2008, we have been arguing roughly — since then, we have been arguing, we have been arguing about this pipeline, but all it's — blocking of the pipeline has really assured is that we're seeing more oil moved by rail. And just in the last two years alone, we have seen in the U.S. 10,000 miles of pipeline be built and globally 23,000 miles of pipeline.

So, in reality, unfortunately, this is just a pipeline, but the symbolism that has been attached to it has far outstripped reality, in my view.

GWEN IFILL: Jeremy Symons?

JEREMY SYMONS, Environmental Defense Fund: Well, the issues are real.

The president did the right thing today. He did the right thing because this is a wrong turn. This pipeline would be a wrong turn for America's energy policy. We're talking about chasing Canada's tar sands oil and we should be focusing instead on the real energy issues in front of the country, which is how we move forward with a clean energy future for America that creates more jobs, that pollutes less and that is abundant.

And I think that that's the debate that Congress is missing and should have had.

GWEN IFILL: But how does this veto allow that conversation to be had?

JEREMY SYMONS: Well, you have to ask yourself why this pipeline for one foreign energy company ended up at the top of the new Congress' agenda, when we have so many energy opportunities in front of us on clean energy.

And the answer is special interests. It took Americans, American families, farmers and ranchers across this country to stand up and shine light on what normally would sneak through in the halls of Washington. But this is a pipeline that is going to last not 10 years, not 20 years, probably 50 years or more.

This is a decision about our children's energy future and we have to take it very seriously and not let this decision go unnoticed.

GWEN IFILL: Robert Bryce, seems like one person's special interest is another person's champion. How does it break down in this case? What would be the wisest step to be taken?

ROBERT BRYCE: Well, I think it's clearly to build the pipeline. Canada is one of — it's our close ally, our neighbor.

This is one of our largest trading partners, and yet we're telling the Canadians essentially to — pardon my language, to stuff it. Look, the idea of trying to block the flow of Canadian oil into the U.S. by blocking this pipeline is akin to trying to make your diet work by shooting the pizza delivery man.

It's not going to work. The reality is blocking the pipeline has resulted in what? Moving more oil by rail. Western Alberta now has over — about 1.1 million barrels of rail terminal capacity in place. In North Dakota — remember, the pipeline is also going to serve the Bakken — they have built about 1.2 million barrels per day of rail terminal capacity.

Keystone is designed to carry 830,000 per day. The idea that blocking this pipeline is going to prevent oil from getting to market is simply false.

GWEN IFILL: Let me ask you about that, Jeremy Symons. You just said there should be a different debate going on. But if it's true that the oil is going to get here perhaps in a less safe way, are you moving toward that debate or away from it?

JEREMY SYMONS: No, it's not about whether there's going to be a less safe way. It's about making choices about what kind of energy future we want to build and infrastructure we want to build.

The reality is that we're seeing already, because of market forces, we have an oil boom, natural gas boom here in America that is contributing to reduced oil prices around the country, around the country. And that is what is standing in the way now of the Canadian — very expensive Canadian tar sands oil.

But it's also a very dirty oil source. So, we have to ask ourselves, this isn't about Canada-U.S. relationships. This is about choosing the path and making sure that Congress and the president are focused on the real opportunities and policy to move beyond the old energy sources and particularly a dirtier source that has 17 percent more greenhouse gas emissions than American conventional oil.

GWEN IFILL: You just mentioned oil prices. Explain to me what the connection between oil prices being depressed and the outcome of this decision today.

JEREMY SYMONS: Well, actually creating this oil from Canadian tar sands is a very energy-intensive, high-polluting process that is also very expensive. And basically they're taking tons of sand and trying to squeeze out a barrel of oil in doing that.

And because it's so expensive, they rely on high energy prices globally to do the big mining investments that they have to, to expand this vast area in the boreal forests of Canada and turn that into mining pits to make this. When you have lower oil prices it is going to put a natural blocker on even the need to have some of this oil come to America.

GWEN IFILL: Robert Bryce, do you draw that same line between decline in oil prices and this outcome today?

ROBERT BRYCE: Well, look, I think your other guest makes a good point.

The decline in oil prices does produce or create some economic challenges for this pipeline, no question about it. It's much more viable, much more profitable for the producers when oil is at $80, than it is when oil is at $50, success as it is now.

But, look, this pipeline is clearly in the national interest. And in his veto statement, the president referred to the national interest a couple of times. Just yesterday, IHS, the consulting firm, said that roughly 70 percent of the oil that would be shipped through Keystone XL would be consumed here in the United States.

I'm for cheap, abundant, reliable energy and I make no apologies for that. This is a good idea for American consumers. To say that we need something else, look, virtually every automobile in the country runs on oil and refined product. To say we are going to shift to something else, well, we may in decades, but this pipeline should be built and it should be built now.

GWEN IFILL: But you started this conversation saying that this is the wrong argument to be having. What difference — how, then, if they were to agree to this pipeline and the president were suddenly to revisit it in the next several weeks, how would that contribute to America's energy independence?

ROBERT BRYCE: Well, look, it would provide more oil to the U.S. market.

We are producing dramatically more oil here in the U.S. We have seen increases of roughly four million barrels of oil per day here in the United States alone. But oil — or gasoline is now at roughly $2. What's wrong with having more oil and reducing the price of oil even further? I see no problem with that.

I think it's a spurious argument to say, oh, we're supposed to shift to something else and reduce our greenhouse gas emissions. The U.S. has reduced its CO2 emissions more than any other country in the world over the last few years, by over 400 million tons. No other country is even close.

GWEN IFILL: Well, go ahead.

JEREMY SYMONS: Well, we agree that the U.S. is reducing our emissions.

In fact, a lot of that is built on the backs of auto workers who have reinvented and auto companies that have reinvented the auto industry to make fuel-efficient cars that pollute less. Why would we move, why would government take on its top priority to bring dirtier fuel to market to put in the tanks of the cleaner cars that we're trying to make?

GWEN IFILL: For today, that's not going to happen. Does that mean that you are optimistic about the president's ultimate decision?

JEREMY SYMONS: I am optimistic. I think he will do the right thing there too. And the case is clear that this is bad for climate, it is bad for our economy, and it is bad for our energy future.

GWEN IFILL: Final word, Robert Bryce.

ROBERT BRYCE: I disagree.

We can talk about climate all day long. If you look at a 2012 study done by Andrew Weaver at the University of Victoria, he was a lead IPCC author. He said — he and a colleague looked at this and said that even if all of the 170 billion barrels of oil in the oil sands of Canada were burned, his quote was the impact in terms of climate change would "be almost undetectable at our significance level."

This climate change argument is a spurious one. Look, again, I will go back to what I said initially. This is about symbolism for the left and for the Democrats. And it's unfortunately become a big fight between the Republicans and the Democrats, when I think this is clearly an infrastructure project that would benefit the U.S. national interest.

GWEN IFILL: It sounds like you both agree on the idea that this is about something bigger, but not on what bigger.

Robert Bryce of the Manhattan Institute and Jeremy Symons of the Environmental Defense Fund, thank you both very much.

JEREMY SYMONS: Thank you.

ROBERT BRYCE: Thank you kindly.