Legislators in both houses of Congress agree that science at the Department of Energy (DOE) should get a slight boost—0.9%—next year. But how they get to that number is quite another story.

This week the full Senate is expected to approve a $5.4 billion budget for DOE’s Office of Science that would eliminate support for an international fusion project in France and trim domestic fusion research. The cuts allow legislators to give relatively healthy boosts to the office's five other research programs within an overall tight budget. To reach the same total, the spending panel in the House of Representatives has proposed continuing to fund ITER and fusion but cutting biological and environmental research and holding the other programs to tiny increases.

For years, observers have been warning that the U.S. commitment to ITER, the gargantuan fusion experiment under construction in Cadarache, France, has been squeezing other DOE basic research programs. That tension shows through clearly in the House and Senate versions of the budget for DOE for fiscal year 2017, which begins 1 October.

The bottom line of $5.4 billion falls far short of the $5.572 billion, a 4.1% increase, sought by the White House. The administration’s request included $125 million for the U.S. contribution to ITER. However, by nixing ITER and trimming domestic fusion, the Senate would manage to give the rest of the Office of Science research portfolio a boost of 4.2%. In contrast, although maintaining the requested amount for ITER and giving fusion a slight increase, House appropriators would give the rest of the office's portfolio only a 0.8% bump.

"The Senate is clearly saying, 'OK, we'll cut ITER and give [the administration] the 4.2% on everything else,'" says Michael Lubell, a lobbyist with the American Physical Society in Washington, D.C. "And the House isn't going along with that."

Under the Senate’s version, which is being debated this week as part of a $37.5 billion appropriations bill covering energy and water programs across the government, funding for fusion energy science would plummet by 36% to $280 million. Even excluding the ITER cut, funding for the domestic part of the fusion budget would fall 13% from current levels. At the same time, the Senate would give the advanced scientific computing research program, which supports DOE's supercomputing efforts, an increase of 5.6% to $656 million—$7 million shy of the requested amount. The basic energy science program, which funds work in condensed matter physics, materials science, chemistry, and related fields, and runs DOE's x-ray and neutron sources, would get a bump of 3.5% to $1.913 billion—$23 million below the request. Nuclear physics would receive a lift of 3.1% to $636 million, as requested. Biological and environmental research would climb 4.6% to $637 million—$25 million short of the request.

The House spending bill has a different vision for energy research. Under its plan, which has not yet been scheduled for a floor vote, funding for fusion would climb 2.7% to $450 million. The total includes $125 million for ITER and a 0.6% increase for domestic fusion research to $325 million. On the other hand, House budgetmakers would keep spending on advanced scientific computing at the current level of $621 million. Spending on basic energy science would inch up 0.6% to $1.860 billion—$76 million short of the request. Spending on nuclear physics would rise 0.5% to $620 million—$16 million short of the request. Spending on biological and environmental research would fall 2.3% to $595 million.

The biggest double winner in the congressional tug-of-war is DOE's high-energy physics program. The Senate would increase spending on high energy physics by 4.8% to $833 million—$15 million more than requested. The House would boost such spending by 3.5% to $823 million.

The two different sets of numbers reflect different priorities, Lubell says. Senate appropriators appear to be trying to fulfill the U.S. pledge made last November in Paris at the international summit on climate change to double funding for energy-related research within 5 years. In contrast, the House seems committed to honoring the U.S. commitment to ITER, which is years behind its initial schedule and far over budget.

Whose vision for the Office of Science will prevail? Although Senate appropriators have tried to kill ITER for 3 years running, Lubell thinks that it's unlikely the United States will pull out of the project. And given that the House and Senate agree on the total for the Office of Science, he expects the final numbers for individual programs to be closer to the House's version. "That 4% increase [for everything else] is not going to materialize," he predicts.

Even bigger squeezes may be on the way, Lubell says. To get ITER done by 2027, the U.S. contribution will have to ramp up to $300 million or more per year. Finding that amount in a constrained budget environment will put even greater pressure on the rest of DOE’s science programs.