WASHINGTON — The Senate Appropriations Committee approved a Pentagon spending bill Thursday that would order more study before the Trump administration can get a new low-yield, tactical nuclear weapon that it wants.

But the measure would have to survive floor consideration and then negotiations to merge the bill with a House version that supports the weapon. The amendment received a bipartisan voice vote of approval from the appropriations panel on Thursday.

“I’m sure that will be looked at on the floor and then in conference, like a lot of things we (the committee) adopt,” panel chairman Richard Shelby, R-Ala., told Defense News afterward. “It might be improved (by an amendment). You never know.”

It’s the latest move in a mostly partisan battle over the deployment of submarine-launched Trident II D5 with a W76-2 warhead.

Congressional Republicans — who have fended off similar legislation in recent weeks — and the Pentagon are advocating for the systems to deter Russia from using its own arsenal of low-yield nuclear weapons. Still, many Democrats and nonproliferation advocates see it as lowering the threshold for a nuclear war.

The amendment, from Sen. Jeff Merkley, D-Ore., prohibits the warhead’s deployment, pending a report from the Defense Department on how to avoid a miscalculation if enemies are unable to distinguish between a low-yield and high-yield missile.

The amendment would also require information on the rationale and planned manning and training changes associated with the weapon.

“My amendment requires a report to be completed to analyze the impacts on strategic stability and deterrence of the low-yield warhead for a submarine-launched ballistic missile,” Merkley said before his amendment was OKed. “It simply requires a report before deployments. It does not obstruct procurement funds.”

Illinois’ Sen. Dick Durbin, the No. 2 Democrat in the Senate and lead Democrat on the defense appropriations sub-panel, told Defense News, “I think when it comes to using and deploying low-yield nuclear devices we need to have a thoughtful approach.”

Joe Gould is senior Pentagon reporter for Defense News, covering the intersection of national security policy, politics and the defense industry.

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