In another sign of Democrats’ move to the left on guns, a group of leading potential 2020 presidential candidates are joining with Hillary Clinton and gun control groups to raise money for Democrats challenging National Rifle Association-backed Republicans in this year’s midterm elections.

Sen. Chris Murphy, D-Conn., organized the one-day effort, which includes some of his most famous colleagues: Sens. Elizabeth Warren, D-Mass., Cory Booker, D-N.J., Kirsten Gillibrand D-N.Y., Jeff Merkley, D-Ore., Tim Kaine, D-Va., and Rep. Joe Kennedy — all of whom have been discussed as potential presidential candidates.

“It’s amazing how this issue has become one of the few litmus test issues in our party,” Murphy said in an interview with NBC News, noting he was advised to avoid talking about guns when he first ran for Congress in 2006. “If you want to be a leader in the Democratic Party, you not only have to have the right position on guns, but you have to be a leader on guns."

Next Friday, the lawmakers will use their large email fundraising lists and social media platforms for a one-day push to raise money for eight House and Senate candidates running against Republicans with perfect ratings from the NRA. The effort, dubbed "NR8" aims to raise at least $1 million for Democrats in seven key battleground House districts and one contested Senate state, Nevada.

After years of being outmaneuvered by the NRA, gun control groups met shortly after the Parkland, Florida shooting this year and agreed to better coordinate their electoral efforts for this year’s elections, instead of pursuing separate strategies.

“This is the first time that we’ve all gotten together, identified a handful of really important races’, and taken the movement for a test drive,” Murphy said, noting his effort includes nearly all the major gun violence group. “I think we’re at a very different moment than we were a few years ago.”