As an energy-efficiency bill heads toward collapse in the Senate, lawmakers and analysts are wondering: If the world's greatest deliberative body cannot pass legislation on energy efficiency, what can it pass? And what will it take?

"We have things that need to be resolved and advanced in the energy sector. If we can't get an energy-efficiency bill to the floor, what does that say about our ability as a Senate to act?" Sen. Lisa Murkowski told reporters before breaking into a coughing fit.

"Speechless," the Alaskan Republican said, after recovering.

But she shouldn't be -- in many ways, what has dogged the bill co-sponsored by Sens. Jeanne Shaheen, D-N.H., and Rob Portman, R-Ohio, for three years is due to sink it again, possibly as soon as Monday.

Republicans wanted to load the measure up with energy amendments on key items for their members. Democrats did not find those amendments germane to energy efficiency, so Senate Majority Leader Harry Reid, D-Nev., blocked them. Reid had offered a standalone vote on whether to approve the Keystone XL oil sands pipeline, which he said was as far as he was willing to go. That, too, is now unlikely to occur.

The Senate hasn't been able to hold a substantive energy discussion on its floor since 2007, largely because of a two-track energy policy process in Washington, coupled with a private sector that has breathed new life into the U.S. fossil fuel industry.

Congress remains gridlocked on energy, not least because of the chasm between the parties over climate change. That has prompted President Obama to go it alone to address greenhouse gas emissions -- but lawmakers on both sides of the aisle who disagree with the push on, say, carbon rules for power plants want to have their voices heard.

"The administration is going to go ahead with its plan, and Congress will continue to want to have its say, and they're not always exactly lined up," said Margot Anderson, executive director of the energy project at the nonpartisan think tank Bipartisan Policy Center.

That's combined with a hydraulic fracturing, or fracking, "revolution" that has turned the United States into an energy powerhouse. The U.S. is projected become the world's largest producer of oil by 2015. It's already become the world's largest natural gas producer thanks to fracking, which blasts a high-pressure cocktail of water, sand and chemicals into tight-rock formations to access hydrocarbons buried deep underground.

So when an energy bill comes to the floor — even an energy-efficiency bill — it's a magnet for other provisions that reflect a changing U.S. energy landscape that has pushed new issues into the forefront for various lawmakers.

"There's a lot of pent-up demand given how the landscape has changed," Joshua Freed, director of clean energy for centrist think tank Third Way, told the Washington Examiner.

That's been visible on Shaheen-Portman, as the energy-efficiency bill is known. These were some of the amendments GOP lawmakers were pushing that might sink the bill: a measure to speed up natural gas export decisions, a policy discussion one never would have envisioned back in 2007 when developers were building import facilities; one to block a carbon tax, arising in the wake of failed cap-and-trade legislation in 2010; and another to scuttle the power plant carbon emission rules.

Reid has been known to "fill the tree," a term for loading up bills with amendments that make only technical changes — changing a three to a four, an enactment date, and so forth — to prevent other lawmakers from attaching measures that might be politically difficult for Democrats. That's been a sticking point for Republicans on more than just energy.

"I'm not open to ratifying Harry Reid's operation of the Senate," said Sen. Johnny Isakson, R-Ga., a Shaheen-Portman co-sponsor, when asked if he would vote to proceed to the bill.

The current state of affairs would change if Republicans retake control of the Senate. Republicans also would get support from a group of centrist Democrats on some energy issues, making it more likely to break through filibusters.

A Republican controlled-Senate, though, might not be a veto-proof Senate. Given the tenor of the amendments GOP lawmakers were offering on Shaheen-Portman, it's unlikely Obama would be eager to sign whatever emerges from Capitol Hill in that scenario.

Sen. John Hoeven, R-N.D., however, sees the most recent kerfuffle as building pressure. He even suggested Republicans don't need to be in the majority to start sending legislation to the White House -- the Keystone XL bill has 57 supporters, 12 of whom are Democrats. And Republicans are primed to pick up a couple seats, as Hoeven singled out West Virginia and South Dakota.

"I'm saying we could even revisit it this year if we don't get it done now," Hoeven told reporters. "And if it doesn't get done this year, I believe it will get done next year because we're only a few votes short and we're going to pick them up."

But Freed, of Third Way, said it will take scaling down the breadth of energy legislation to see any progress in the Senate.

"This should all be done separately. That's likely to be the way over the next couple of years to see the deadlock on energy get broken," Freed said.

Added Anderson, of Bipartisan Policy Center: "Patience is wearing thin."

That's why Sen. Ron Wyden, D-Ore., who was chairman of the Senate Energy and Natural Resources Committee when it heard the bill last year, said working on energy issues in piecemeal is the proper way to advance policy. He pointed to hydropower legislation the Senate passed last year, which sailed through the upper chamber without a fuss.

"What the majority leader did was make it clear he wanted to meet my colleagues on the other side halfway and said there will be a vote on Keystone, and that was, as you know, for many, many months that was the big interest," Wyden said. "And now there are other issues involved."

Republicans, however, are more incensed over process. They have long objected to how Reid has conducted floor proceedings on energy and other policy matters.

On Shaheen-Portman, Republicans said Reid knew their demands all along, and that a straight vote on the bill in exchange for a Keystone XL vote was not their main play.

"I don't know how anybody could not have understood that this was a critical part of us wanting to and being willing to go forward," said Sen. Roy Blunt, R-Mo., a member of Senate GOP leadership.

Now, it's going to take some time before senators attempt to brave the energy debate again.

"In this kind of environment, it's fairly hard to get both sides to agree to order a Coca-Cola," Wyden said.