Republican likely presidential hopefuls have united in opposition to the New Strategic Arms Reduction Treaty (START), which could make the agreement with Russia a 2012 campaign issue.
South Dakota Sen. John Thune (R) was the latest to offer his criticism.
"First and foremost, missile defense remains a major point of disagreement between the United States and Russia, and this treaty only makes the situation worse," he wrote in an opinion piece for National Review Online.
Former House Speaker Newt Gingrich (R-Ga.) predicted it would be an issue for voters in 2012.
"This will be a big issue because as a consequence of this treaty, President Obama will continue to undermine missile defense," Gingrich told The Associated Press. "It's an obsolete approach that's a holdover from the Cold War and a bilateral treaty without taking into account multilateral threats."
Gingrich and Thune join Mitt Romney, Tim Pawlenty and Sarah Palin as critics of the agreement.
The treaty would see the United States and Russia eliminate hundreds of nuclear weapons from their aging stockpiles. Obama has urged the Senate to pass the agreement during its lame-duck session, but some Republicans have complained there isn't enough time for that to happen.
--Updated at 6:18 p.m.