In a strongly-worded open letter, six Democratic senators demanded Thursday that Supreme Court nominee Neil Gorsuch disclose the identities of donors behind the right-wing dark money group spending millions to push for his confirmation.

The letter (pdf), signed by Sens. Sheldon Whitehouse (D-R.I.), Diane Feinstein (D-Calif.), Richard Durbin (D-Ill.), Al Franken (D-Minn.), Richard Blumenthal (D-Conn.), and Mazie Hirono (D-Hawaii), pointed out that because the Judicial Crisis Network (JCN) "is not required to disclose the identities of its donors, the American people have no idea who is so aggressively advocating for your confirmation, or why."

During his confirmation hearing earlier this month, Gorsuch refused to answer questions about the identities of JCN's funders. "You'd have to ask them," he said.

"We have now done so," the Senators wrote in their letter. "It is your nomination that is before us, however, and we look to you to clarify concerns about it. You assured our Committee last week that, despite the unprecedented flow of dark money in support of your candidacy, 'nobody will capture me.'"

The letter continues:

To that end, we ask that you answer the following questions prior to the Committee's anticipated vote on your nomination:

1. Will you ask JCN to disclose the identities of its donors in order to put to rest any concerns that donations made in secret could affect your rulings?

2. Should you find out the names of individuals or organizations who contributed to the the JCN's, or any other campaign in support of your confirmation, will you pledge to disclose them to the American people?

3. Should you find out the names of individuals or organizations who contributed to the JCN's, or any other campaign in support of your confirmation, will you pledge to a) make public any cases in which they appear as litigants and b) consider recusal even if the formal rules of Supreme Court do not mandate it?

During his confirmation hearings, Gorsuch wasn't only slippery during his answers to questions on his ties to dark money. The judge also refused to outright state his stance on critical Supreme Court decisions certain to face challenges in upcoming years, such as Roe v. Wade.

"If Judge Gorsuch wasn't the least forthcoming Supreme Court nominee ever to appear at a confirmation hearing, it's hard to imagine one who could be less forthcoming while still breathing. More interesting and less predictable answers could have come from Siri on an iPhone," wrote the New York Times' Linda Greenhouse.

Gorsuch's refusal to discuss his judicial philosophy and the right-wing dark money funders pushing his nomination, as well as his failure to even meet with some Democratic senators have all contributed to swiftly falling Democratic support for the conservative judge's nomination.

Sen. Tammy Duckworth (D-Ill.) became the latest Democrat in the Senate to announce her refusal to support Gorsuch on Thursday. As of Friday, 34 Democrats have vowed to block Gorsuch and the number is rising. Forty-one votes are required to prevent the super-majority vote that would end debate on Gorsuch's nomination. Senate Minority Leader Chuck Schumer (D-N.Y.) signaled last week that he would support a filibuster against the right-wing nominee, while several Democrats remain undecided, as Common Dreams reported.

Only two Democrats, the right-leaning Sens. Heidi Heitkamp (N.D.) and Joe Manchin (W.Va.), have announced their support for Gorsuch. If Gorsuch doesn't garner 60 votes in the Senate, Republican leaders have said that they may trigger the so-called "nuclear option," and change the rules to require a simple majority for a Supreme Court nomination to move forward.

Meanwhile, the popular resistance to Gorsuch's nomination is growing. Progressive groups are petitioning the Democratic Senatorial Campaign Committee to publicly announce that it will not allocate funds for Democrats who support Gorsuch, and on Saturday, people are taking to the streets in cities across the country for a "People's Filibuster" against Gorsuch and President Donald Trump.

The People's Defense campaign, which is organizing the nationwide action, writes that the filibusters will feature "everyday Americans speaking about why they object to President Trump's radical, out-of-touch agenda, his desire to overturn Roe v. Wade, his unconstitutional travel ban, and his selection of Neil Gorsuch for the Supreme Court."

Find a People's Filibuster near you here.