A dark money led-coalition of more than 100 liberal groups is ramping up calls for Democrats to nuke the 60-vote Senate threshold following the blockade of a commission to investigate the Jan. 6 Capitol riot.

Fix Our Senate, the coalition's leader, on Thursday sent a letter to Senate Majority Leader Chuck Schumer, D-N.Y., with the renewed calls. The letter, however, appears geared toward pressuring Sen. Joe Manchin, D-W.Va., into supporting the elimination of the filibuster. 

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"We have moved past hypotheticals and entered a perilous new moment for our democracy," reads the letter, first obtained by NBC News. "Senate Republicans' decision to block legislation establishing a bipartisan commission to investigate the January 6th insurrection is a shameful abdication of their duties to our country. As Senator Joe Manchin said, 'So disheartening. It makes you really concerned about our country.'" 

"That Republicans could not even support a bipartisan investigation into a deadly attack on the U.S. Capitol reflects dangerously misplaced priorities: they have chosen party over country, obstruction over progress, and Trump over democracy. In the face of Republicans’ inability and unwillingness to defend our democracy, it is clearer than ever that the filibuster needs to be eliminated."

WASHINGTON, DC - MAY 28: Sen. Joe Manchin (D-WV) talks with reporters after stepping off the Senate Floor at the U.S. Capitol on May 28, 2021 in Washington, DC. The Senate decided to postpone debate on the act after a small group of Republicans filibustered the bill overnight. The Senate also failed to reach the 60 votes necessary to end debate on the legislation that would approve the formation of a 9/11-style commission to investigate the attack lead by Trump supporters on the Capitol to attempt to halt the certification of the 2020 presidential election. (Photo by Chip Somodevilla/Getty Images) ((Photo by Chip Somodevilla/Getty Images))

Manchin has stated he opposes eliminating the filibuster and moving to a 50-vote threshold to advance legislation. He has been a primary target of liberal groups since Democrats took back control of the Senate and presidency.

The leader of the push to nuke the filibuster, Fix Our Senate, is at the Sixteen Thirty Fund, a dark money fund managed by D.C.-based consulting firm Arabella Advisors. Arabella-managed funds, which each include dozens of liberal nonprofits, have turned into a powerhouse. Anonymous wealthy donors have used the network to push more than $1 billion into progressive endeavors in recent years. 

The anti-filibuster coalition has added more than 40 groups since March. Others in the coalition include liberal watchdog Citizens for Responsibility and Ethics in Washington, Indivisible, Demos, Greenpeace, March for Our Lives, MoveOn, and the Sunrise Movement. In addition to Fix Our Senate, dozens of other groups in the coalition are funded by anonymous cash.

The coalition has attacked the filibuster as a racist tool and "Jim Crow relic," a phrase used by former President Barack Obama and adopted by progressive activists and other Democrats.

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"We want to make sure voters understand that the filibuster, an abused and outdated ‘Jim Crow relic,' is a big part of what is broken about our government and we are encouraging them to make their voices heard and call on their senators to choose progress, not more gridlock," Eli Zupnik, a spokesperson for Fix Our Senate, has said of the efforts.

Democratic politicians such as Sen. Elizabeth Warren, D-Mass., and Reps. Cori Bush, D-Mo., and Pramila Jayapal, D-Wash., have called the filibuster racist.

Fix Our Senate did not respond to a request for comment by the time of publication.