(CNN) - A congressional effort to bypass the White House and approve the controversial Keystone XL pipeline appears likely to fizzle this week, CNN has learned.
The development comes after three Democratic senators, who cast their support previously for the long-delayed, cross-border pipeline, said they would vote against the legislation.
Such an outcome would be a victory for the Obama administration, which is reviewing environmental concerns about the politically-charged energy project.
Simply moving forward with the vote also would be a political boost for several red-state Democrats facing tough re-election battles who support the pipeline and who want to prove to their constituents that they did everything possible to get it approved.
TransCanada wants to complete a pipeline from northern Alberta to the Gulf Coast that would carry the tar sands oil across six U.S. states.
The $5.3-billion project needs federal approval because the pipeline would cross an international border. For now, the review rests with the State Department, headed by Secretary of State John Kerry.
He will ultimately deliver a recommendation to President Barack Obama, who will make a final decision.
Senate Majority Leader Harry Reid, a Keystone opponent, surprised many when he said last week he was open to allowing a vote on the legislation in the coming days.
But now his strategy is becoming clearer - allow a vote that would fail in the Senate, but succeed in giving political cover to some of his most endangered Democratic colleagues - those who if they lose in November could mean a Republican takeover of the Senate.
Senators like Mary Landrieu of Louisiana, Mark Begich of Alaska, John Walsh of Montana, and Mark Pryor of Arkansas, could tell voters they fought hard for one of the energy industry's top priorities and the accompanying jobs that would go with it.
The Keystone proposal, written by Sen. John Hoeven, R-North Dakota and Landrieu, has 56 co-sponsors - 45 Republicans and 11 Democrats. That is still four short of the 60 votes it would need to pass.
Hoeven said last week he hoped to pick up additional votes from Democrats he described as open to voting for the pipeline.
Those votes would likely have to come from six other Democrats who just over a year ago backed a non-binding measure that expressed support for the project.
Of that group, Senators Bill Nelson of Florida, Chris Coons of Delaware, and Tim Johnson of South Dakota, citing different reasons, now say they will vote against the current legislation, making it unlikely it would reach the 60-vote threshold.
None of the three face the same political pressures as the red-state Democrats running for re-election, making it easier for them to oppose the bill. Johnson is retiring and Nelson and Coons come from less conservative states.
In a statement, Johnson said, "the recent Nebraska Supreme Court decision that invalidates the pipeline's route through Nebraska has created significant uncertainty at the state and federal level."
An aide to Coons said the senator is "frustrated with how long it's taking for a decision to be made, but he doesn't think it's Congress' role to be issuing construction permits."
And an aide to Nelson said while the senator supports the Keystone pipeline, he wants to pass an accompanying law ensuring the oil that goes through it is used at home and not exported.
As to the other three Democratic senators who voted in favor of last year's measure, only Sen. Bob Casey of Pennsylvania said he would support the current bill.
An aide to Sen. Michael Bennet of Colorado wouldn't say which way he would vote. An aide to Sen. Tom Carper, D-Delaware, said the senator is still deciding how he will vote.