Republicans thwarted a bipartisan attempt to restrict secret holds in the Senate on Thursday night, arguing that the measure was unrelated to the financial reform bill the Senate was considering.

The Senate was expected to vote Thursday afternoon on an amendment by Sens. Ron Wyden (D-Ore.) and Chuck Grassley (R-Iowa) restricting secret holds. But Wyden chose to withdraw the measure after Sen. Jim DeMint (R-S.C.) said he would attempt to attach to it language requiring construction of a 700-mile security fence along the Southwest border.

“Until about an hour or so ago, I thought we would win a dramatic victory for the cause of open government,” Wyden said on the floor, adding that he was “flabbergasted” that DeMint pushed his security amendment, which would have made it impossible to pass the provision on secret holds.

A senior GOP aide said DeMint chose to push his measure because Democrats “degenerated the amendment process into one with a bunch of off-topic political votes.”

Democrats acknowledged that they feared a politically motivated amendment like DeMint’s would emerge if Wyden’s proposal — also off-topic to the financial reform issue — made its way to the floor.

A handful of Democrats went to the floor after the chamber wrapped up business for the night to blast DeMint’s move and again call for an end to secret holds. Sen. Claire McCaskill (D-Mo.) has convinced 60 colleagues,

including Grassley and Sen. Scott Brown (R-Mass.), to sign a letter promising not to secretly hold any legislation or nominations pending in the Senate.