Accountable.US is a center-left advocacy group and self-described “nonpartisan watchdog group.”
The group is a project of the New Venture Fund, a center-left 501(c)(3) nonprofit managed by the Washington, D.C.-based philanthropy consulting firm Arabella Advisors, though Accountable.US has announced that it is “in the process of transitioning from the New Venture Fund” into a standalone nonprofit. 
Accountable.US’ board members have extensive connections to Democratic officials and causes, left-wing advocacy groups, and in particular other left-wing “accountability” organizations that dovetail with the mission laid out in the January 2017 Brock proposal. Three board members have history with American Bridge 21st Century and Citizens for Responsibility and Ethics in Washington (CREW) – the two main organizations specifically promoted in the Brock proposal.  
Kyle Herrig is currently the president and founder of Accountable.US and previously worked on the advisory board of Restore Public Trust. He is the director of New Venture Fund and is on the board of American Oversight.  He co-founded and is an advisor for Allied Progress, Equity Forward, and Fix the Court. 
Shripal Shah is currently on the advisory board of Accountable.US and previously worked on the advisory board for Restore Public Trust.  He is vice-president of American Bridge 21st Century, a Democratic Party super PAC. He was formerly a staffer for the Democratic Senatorial Campaign Committee (DSCC), the Democratic Congressional Campaign Committee (DCCC), and the Democratic National Committee (DNC). In 2014, he worked as both communications director and deputy campaign manager for Senator Jeanne Shaheen. 
Brad Woodhouse is currently on the board of Accountable.US and previously worked on the advisory board for Restore Public Trust.  He is executive director of Protect Our Care, an Obamacare advocacy organization and project of the Sixteen Thirty Fund, a 501(c)(4) advocacy group and sister to New Venture Fund. He is also a former president of both American Bridge 21st Century and Americans United for Change, and a former communications staffer for the Democratic National Committee (DNC). He worked as an advisor and a spokesperson for Senator Jon Corzine in the early 2000s, a communications director for the Democratic Senatorial Campaign Committee in 2003-2004 and as communications director for the Democratic National Committee in 2008. He also worked as a senior strategist for both of President Obama’s campaigns in 2008 and 2012. 
Melissa (Bruns) Bonine’s RPT bio refers to her as an operations expert for center-left groups. She has a work history that includes the offices of congressional Democrats and in the Obama administration.