Ohio Republican Sen. Rob Portman has spent months lauding his energy efficiency bill as a model for bipartisan cooperation, carefully garnering the support of more than 260 groups as diverse as the Christian Coalition and the left-leaning environmental group, Earthjustice.

But a series of controversial amendments threaten to sink his bill, which Portman first started pushing with Sen. Jeanne Shaheen, D-N.H., back in 2011.

Sen. David Vitter, R-La., has ground the proceedings to a halt by blocking other senators from calling up their amendments to Portman’s bill until Vitter is guaranteed a vote on a measure related to President Obama’s health care bill. Portman, for his part, says he believes Vitter’s amendment deserves a vote.

But that’s only the first fight. Even presuming the Senate manages to iron out the Vitter spat, an amendment over the controversial Keystone XL pipeline awaits.

Portman’s bill – which he’s described as an example of Senate cooperation – may ultimately be sunk by fellow members of his party.

The Shaheen-Portman bill would, among other things, strengthen building codes to make new homes and commercial buildings more energy efficient. It directs the Department of Energy to work closely with the private sector to encourage research and development of energy efficient technology and processes. And it would create a Department of Energy program – SupplySTAR – to help make companies’ supply chains more efficient.

Vitter’s amendment is a response to a recent White House decision that would allow the federal government to continue to contribute to lawmakers’ and aides’ health care coverage. His measure would undo that ruling, and also require White House officials and political appointees to participate in the health care exchanges created by the 2010 health care law.

Vitter admits his amendment has little to do with the Portman legislation. But he argues time is running out because many of the controversial provisions of the health care law go into effect Oct. 1.

Time may be running out on the Shaheen-Portman bill as well. Congress has until Sept. 30 to approve a spending bill that will keep the government open. In a conference call last week, Portman remained hopeful that the bill will go to the president’s desk for a final signature by the end of the year, but he said the biggest risk is that the bill will be overtaken by the urgency of the budget process.

Ross Baker, a political science professor at Rutgers University, said Vitter has attached a “poison pill” to the energy efficiency bill.

He said Vitter’s move will sacrifice floor time for Portman’s bill – and “floor time in the Senate is the most precious commodity you have.”

“Obviously for Sen. Portman it would be a real feather in his cap in a Congress that hasn’t done very much to be associated with something that really goes some place,” he said.