Six Democrats who voted for the Keystone XL pipeline at least once are up for re-election in 2014 -- and they may throw environmentalists under the bus to boost their chances.

The move could force President Obama's hand in approving the pipeline, which environmentalists have opposed, claiming great risk to the environment and water supplies.

Republicans need to pick up six seats in 2014 to retake control of the Senate, and it already appears that the Democrat strategy to keep control will involve getting as far away from Obama's policies -- especially Obamacare -- as possible. Republicans need to defend 14 Senate seats, while Democrats have to defend 21 seats in order to keep control.

Democratic Sens. Mark Begich of Alaska, Chris Coons of Delaware, Kay Hagan of North Carolina, Mary Landrieu of Louisiana, Mark Pryor of Arkansas and Mark Warner of Virginia all voted in favor of building the Keystone pipeline in March 2013 and are up for re-election.

Begich is defending his seat in Alaska, a state Obama lost in 2012 by 14 points. Begich also voted for Obamacare but tries to portray himself as a state advocate by working to advance oil extraction. A GOP civil war in the region may be his only hope.

Hagan was elected in the 2008 Obama wave, but since then the state has skewed Republican. Hagan also voted for Obamacare and may benefit from a GOP intraparty war.

Landrieu also supported Obamacare but hasn't run from the law like many other Democrats. Instead, she's focused her campaign on fixing the law. And yet again, GOP infighting might help her hold on to her seat.

Pryor might be the most vulnerable, according to Politico. Obama lost Arkansas by 24 points in 2012, and Pryor voted for Obamacare. Pryor's Republican challenger, Rep. Tom Cotton, R-Ark., does not have to worry about infighting and is slightly ahead in the polls.

Coons and Warner appear to be safe in their respective states, although both supported Obamacare, but the entry of GOP strategist Ed Gillespie in the Virginia race could be a sign that party leaders see Warner as vulnerable.

Begich, Hagan, Landrieu, Pryor and Warner also parroted Obama’s “if you like your plan, you can keep your plan,” lie.

Meanwhile, retirement of Democratic Sens. Max Baucus of Montana and Tim Johnson of South Dakota — both of whom voted for the pipeline — leave openings for other candidates who may also support Keystone.

In Montana, Baucus' nomination as ambassador to China meant the governor would have to appoint an interim senator -- nd all signs point to Democrat Lt. Gov. John Walsh getting that appointment. Walsh is a big supporter of Keystone.

In South Dakota, Republicans are expected to easily pick up Johnson’s now open seat in a state Obama lost in 2012 by 18 points.

Those states value oil and natural gas, and Democrats running will most likely position themselves as pro-conventional energy. Pushing for Keystone might be their best bet, said Sen. John Thune, R-S.D.

“High unemployment and stagnant economic growth have contributed to the growing number of Americans who support the construction of the Keystone XL pipeline,” Thune said. “Its construction would support thousands of jobs and invest billions of dollars in the U.S. economy.”

“Congressional Democrats and the president would be wise to stop pandering to the far-left environmental donor base and instead start considering what is right for the American people,” Thune said.

Democrats will have trouble showing that they are “pro energy” and “pro jobs” without supporting the pipeline. And distancing themselves from the environmentalists trying to delay or block Keystone will be a hit to base supporters.

Obama has thus far given lip service to both environmentalists and pipeline supporters — and has ducked the issue time and again, but he may have to cave in order to protect his party's control of the Senate.