The Senate barely killed an amendment yesterday to override President Obama on the Keystone XL pipeline, raising a new political headache for the White House in an election year.

In a 56-42 vote, 11 Democrats joined Republicans in supporting a measure attached to a transportation bill that would have authorized construction of the Canadian oil conduit, despite Obama's denial of a cross-border permit for it earlier this year. If two absentee senators had voted, the outcome likely would have been two votes shy of the needed passage number of 60.

As has been the case for weeks, Republicans signaled they would not let the issue go away. Sen. Richard Lugar (R-Ind.), a co-sponsor of the amendment that failed, said he would try to push Keystone XL forward at "every available turn."

"When it comes to delays over Keystone, anyone looking for a culprit should now look no further than the Oval Office," said Minority Leader Mitch McConnell (R-Ky.) in a statement after the vote. He and other GOP members slammed the president all day, after Politico reported that Obama was lobbying senators before the vote.

The Democrats voting for the amendment were Sens. Max Baucus of Montana, Mark Begich of Alaska, Robert Casey of Pennsylvania, Kent Conrad of North Dakota, Kay Hagan of North Carolina, Mary Landrieu of Louisiana, Joe Manchin of West Virginia, Claire McCaskill of Missouri, Mark Pryor of Arkansas, John Tester of Montana and Jim Webb of Virginia.

Before the vote, White House spokesman Jay Carney slammed senators for playing politics with a pipeline that would not affect oil prices in the short term and does not yet have a full route around Nebraska's Sandhills. "We'll keep making that point in telephone calls from the podium, maybe fly a Cessna overhead with a banner -- something like that," he said.

It is not a coincidence that the Senate vote was so close at a time when many voters are putting gas prices at the top of their concerns in swing states, said Kenneth Green, an analyst at the American Enterprise Institute. He pointed to a CBS poll showing that more than 70 percent of individuals in seven states voting for presidential candidates Tuesday said rising gas prices were an important factor in their votes.

A Gallup poll released yesterday also found that a gas price of $5.30 per gallon could be a tipping point for most voters in terms of prompting significant life changes. Even at an average gas price of $4 to $5, 28 percent of voters said they would be forced to make significant cutbacks in their spending, according to Gallup.

A link to high gas prices?

Green groups are making the case vigorously that the debate over gas prices in relation to Keystone XL is absurd, considering that oil sands crude carried from Canada's oil sands region via existing pipelines currently is sold at a discount in the Midwest.

Building Keystone XL would actually send prices higher by relieving that oil glut, they say. It also would set up the crude for potential export, they say.

"This dirty energy project would worsen climate change, have a high chance of oil spills, and raise oil prices -- all so that tar sands companies can export tar sands from the Gulf," wrote Susan Casey-Lefkowitz of the Natural Resources Defense Council in a blog post after the vote. The oil from Canada's oil sands region releases more greenhouse gas emissions in the production process than do traditional forms of oil, another point of contention among environmental activists.

An amendment offered by Sen. Ron Wyden (D-Ore.) that would have restricted the export of oil refined from Keystone XL also failed yesterday, 34-64. On the Senate floor, Wyden said he believed the pipeline would lead to higher prices for American business and consumers.

Pipeline supporters, on the other hand, maintain that the pipeline would place downward pressure on oil prices over time by adding global supply.

The politics remain potent

Amid the political backdrop, 350.org -- the group that led anti-Keystone XL protests at the White House last year -- said it would be organizing events around the country during the upcoming congressional recess to get every member of Congress on the record about fossil fuel subsidies generally. "We'll be keeping a close eye on any further attempts to revive the Keystone XL zombie, but for now, it's time to go on the offensive again," said Jamie Henn, a spokesman for the group.

The environmental argument about Keystone XL raising gas prices could be a tough sell for voters, said Julian Zelizer, a professor at Princeton University. The argument about a glut in the Midwest and current oil discounts there is the kind of "three-step" complicated reasoning that does not tend to stick with the average person scanning the news, he said.

"The Republicans may have a winning argument on this," regardless of whether it is true, he said. At the same time, he said he did not think the pipeline would be a decisive campaign issue unless gas prices shot much higher. If that happened, then Obama might have to weigh state by state how much he would have to gain from environmentalists versus independent voters, another analyst said.

But several Democrats on Capitol Hill yesterday dismissed any peril for Obama. Sen. Tom Carper (D-Del.) said "no" emphatically when asked whether the constant pressure from Republicans on the pipeline posed any risk for the president or Democrats.

"This is a completely trumped-up, phony issue" that voters can see through, said Sen. John Kerry (D-Mass.) about Keystone XL.