This really cost us Keystone approval: Democratic senator

Sen. Heitkamp: Nebraska lawsuit likely stopped Keystone
Keystone... it's a pipeline not a cause: Sen. Heitkamp
Keystone's carbon issues

Sen. Heidi Heitkamp from North Dakota, a long-time Democratic supporter of the Keystone XL pipeline, told CNBC on Wednesday that approval for the project may have failed this time around, but it will pass next year when Republicans take control of the Senate.

The legislation that fell short in the Senate and passed last week in the GOP-controlled House would have bypassed the federal review process on the Alberta, Canada-to-Nebraska pipeline, which is currently being held up by a pending Nebraska Supreme Court decision. A state lower court ruling invalidated the governor's decision to allow the Keystone XL pipeline to pass through Nebraska.

"We could have probably picked up a couple more [votes] had that process been completed," Heitkamp said in a "Squawk Box" interview. "The question is what is the president going to do with it once the Nebraska decision comes through. What's his final decision going to be? And then if he decides to veto … do we have enough votes to override?"

The Democrat-controlled Senate Tuesday night was one vote short of the 60 votes required to approve the pipeline, which TransCanada first proposed in 2008 to help transport oil from the Bakken region — encompassing parts of Canada, Montana and North Dakota.

"It's a pipeline. It shouldn't be a cause. It's an essential piece of the infrastructure," said Heitkamp, who argued that the project would help keep gas prices lower by enabling easier access to oil supply.

Read MoreSenate defeats Keystone XL pipeline

When the House approved its version of the Keystone XL pipeline bill on Friday, it did not pass with enough votes to override a presidential veto.

Next year, that won't change, predicted Greg Dotson, energy policy vice president at the liberal think tank Center for American Progress. "It doesn't appear there are enough votes to override a veto in either the House or Senate," he said. "So the decision is going to still reside with the president."

The Keystone XL pipeline was put on the front burner again as both sides in the December runoff Louisiana Senate race (incumbent Democrat Sen. Mary Landrieu and Republican challenger Rep. Bill Cassidy) sought the advantages from being seen to support a project that backers believe would create more jobs in America's energy boom. Oil is already flowing from the southern parts of TransCanada's network, a short pipeline extension from Nebraska to Oklahoma and the longer Oklahoma-to-Texas stretch.

Earlier in the year, the State Department concluded that the Keystone XL project would create 42,100 jobs during the construction phase and about $2 billion in economic benefit.

Critics of the pipeline have cited environmental concerns, and they've called into question the staying power of those estimated jobs. Dotson told CNBC that the negative environmental impact "ultimately proved to be a compelling argument" against the pipeline in Tuesday's Senate vote.

Cindy Schild, head of refining issues at the energy trade association American Petroleum Institute, countered on "Squawk Box," arguing that a number of environmental reviews have showed minimal impact.

She also said it's in the national interest. "It is time to build this pipeline. The economic benefits, the energy security benefits, the national security benefits are tremendous, especially when we can secure our consumers and our ability to refine oil here in this country from North American sources."

Wire services contributed to this report.