A Liberator pistol appears next to the 3-D printer on which its components were made in Hanover, Md., in 2013. (Robert MacPherson/AFP/Getty Images)

A Democratic senator on the Foreign Relations Committee is blocking the nomination of a key State Department nominee until the Trump administration fully scraps plans to allow an organization to post online blueprints for 3-D-printed guns.

A federal judge in Washington state on Tuesday temporarily blocked an agreement with the State Department that would have allowed Texas-based Defense Distributed to publish documents that include instructions for making the guns with a 3-D printer. Gun control advocates, including many Democratic lawmakers, have argued that the documents could be used by bad actors, including terrorists, to print plastic firearms that could evade detection by traditional security measures.

On Wednesday, Sen. Edward J. Markey (D-Mass.) informed R. Clarke Cooper, who is nominated as the next assistant secretary of state for political-military affairs, that he would be objecting to his confirmation until the administration reverses its policy. Cooper would have authority over the Directorate of Defense Trade Controls, the government office that reached a settlement with Defense Distributed that would have allowed it to post the blueprints.

“I appreciate that you are not the person who made this policy, but you are asking us to confirm you to a position where you will be defending the indefensible,” Markey told Cooper during a hearing to consider his nomination Wednesday. “Until the president agrees to reverse this policy and prohibit the online publication of these dangerous blueprints, a decision that is entirely within his authority, I intend to place a hold on your nomination.”

Any senator can prevent a nomination from quickly proceeding to confirmation by placing a “hold” on that nomination. Absent a federal judge’s order preventing the publishing of the documents, Defense Distributed was expected to post the instructions online Wednesday.

“We cannot rely on the courts to keep saving us from the excesses and mistakes of this administration,” Markey said.