In this Feb. 9, 2017, file photo, Attorney General Jeff Sessions holds a meeting with the heads of federal law enforcement components at the Department of Justice in Washington. Associated Press/Susan Walsh Attorney General Jeff Sessions has faced mounting calls in recent days to recuse himself from any investigations into Russian ties to Trump's former National Security Advisor Mike Flynn and other aides and Trump's 2016 presidential campaign, but has so far remained unpersuaded.

On Wednesday, for the second day in a row, Senate Minority Leader Chuck Schumer demanded an investigation into Russian ties to Trump associates conducted by an "independent and unbiased law enforcement authority" that explicitly excludes Sessions.

"The new Attorney General Jeff Sessions cannot be the person to lead that investigation … it is a clear conflict of interest," Schumer said on the Senate floor, citing Department of Justice regulations.

"The words are crystal clear. There is no wiggle room … Any investigation headed, directed by, or influenced by the Attorney General will be jaundiced from the very start."

But Sessions has previously said he sees no need to recuse himself from any such investigations, and one of his advisers told the New York Times he has not been swayed from his position by recent events.

The Justice Department's rule on the matter is brief: "No DOJ employee may participate in a criminal investigation or prosecution if he has a personal or political relationship with any person or organization substantially involved in the conduct that is the subject of the investigation or prosecution, or who would be directly affected by the outcome."

The regulation then defines "political relationship" as a "close identification with an elected official, candidate, political party or campaign organization arising from service as a principal advisor or official."

Democrats have argued that Sessions' role alongside Flynn on the National Security Advisory committee during the transition, his position as senior adviser in the Trump campaign, and his enthusiastic endorsement and nomination of Trump at the Republican National Convention last summer constitute a "political relationship" that would interfere with the integrity of an investigation.

"The rules requiring Sessions to recuse from the Trump campaign investigation are so clear you have to question why he is refusing to do so," Matthew Miller, a former spokesperson for former Attorney General Eric Holder, tweeted on Tuesday.

The conflict of interest isn't confined to Sessions' close political relationship with Trump, according to David Alan Sklansky, a former federal prosecutor and current Stanford law professor. Sessions also made public comments during the campaign praising Trump's "pragmatic" approach to Russia.

"It is hard to imagine how his own name — not just the name of the President who appointed him — can fail to surface in this investigation, and hard to imagine how the investigation can fail to touch on, if not Sessions' own actions, at a minimum the actions of close political associated of his in 2016," Sklansky wrote.

Democrats first issued the demand on Tuesday, the day after Flynn resigned over his communications last December with the Russian ambassador. Later that day, the New York Times reported that intercepted phone calls revealed that Trump's associates and campaign staffers had repeatedly communicated with senior Russian intelligence officials in 2016.

Schumer was not alone — 11 Democratic senators on Wednesday jointly called for Sessions to appoint an independent special counsel to investigate Flynn's communication with Russian officials, so as to "maintain the confidence, credibility and impartiality of the Department of Justice."

Debate over Sessions' role in forthcoming investigations was anticipated by Democratic senators during Sessions' confirmation last month, during which Senator Dianne Feinstein of California noted the close working relationship Sessions would have with Flynn upon his confirmation as Attorney General, and asked if he would recuse himself from an investigation.

Sessions replied that he was "not aware of a basis to recuse" himself, adding that he would consult with DOJ ethics officials if he felt his impartiality "might reasonably be questioned."

Sessions did, however, say he would recuse himself from any investigations related to Hillary Clinton's use of a private email server or any matters regarding the Clinton Foundation, given that he had previously made critical comments that "could place my objectivity in question."

Here's Minority leader Schumer speaking on the Senate floor: