(CNN) The Trump administration has tapped Marshall Billingslea, the current undersecretary for terrorism financing at the Treasury Department, as special envoy for nuclear talks, according to two sources familiar.

The decision comes nearly one month after US national security adviser Robert O'Brien said the US was preparing to begin negotiating a new nuclear arms agreement with Russia.

The National Security Council declined to comment and Billingslea hasn't responded to CNN's inquiry.

Billingslea had previously been nominated to be under secretary for civilian security, democracy and human rights at the State Department but his confirmation process stalled after Democrats and advocacy groups raised concerns about his views on torture while working for President George W. Bush's administration. As of Wednesday evening, a Democratic Senate aide told CNN that the nomination had not yet been formally withdrawn.

"There has been ample evidence that Mr. Billingslea encouraged the use of interrogation methods that amount to torture or other cruel, inhuman, or degrading treatment while he served in the Bush Administration," Daphne Eviatar, director of security with Human Rights at Amnesty International USA, wrote last September. "This makes a mockery of that important position."

During his confirmation hearing last year, Billingslea told lawmakers that he would "advocate for and respect" Congress' 2015 decision to ban torture.

Daryl Kimball, the director of the Arms Control Association, noted Billingslea's history as an aide to former Sen. Jesse Helms, a North Carolina Republican who was a vocal opponent of arms control deals . Kimball told CNN that Billingslea was "an odd choice" for the role of special negotiator

Last month, O'Brien said that the US was going to "confront the Russians ... but at the same time I think we'll negotiate," while speaking at the Meridian International Center in Washington to ambassadors from around the world.

O'Brien gave that speech as the US and Russia hit the one-year deadline to extend the New START Treaty, the last legally binding agreement limiting their nuclear arsenals -- the world's largest.

President Donald Trump has previously criticized new START as a "bad deal" and the administration has demonstrated a pattern of rejecting international agreements, including two other nuclear pacts, the Intermediate Range Forces Treaty and the Iran nuclear deal.

Kimball said it may be a "suicide mission" if Trump wants Billingslea to deliver progress on a trilateral arms agreement, especially given that the Chinese have said multiple times that they're not interested in negotiations while there's such a disparity in the arsenal sizes between them and the US and Russia.