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 was the senior Pentagon reporter for Defense News, covering the intersection of national security policy, politics and the defense industry. He had previously served as Congress reporter.

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