According to RollCall, Connecticut Senator Chris Murphy’s gun control project is backing Anna Throne-Holst:
“… Murphy’s Fund to End Gun Violence will also be backing … Anna Throne-Holst, the former Southampton town supervisor challenging GOP Rep. Lee Zeldin in New York’s 1st District on Long Island. “I’m proud to support … Anna Throne-Holst because they’ve made ending gun violence cornerstones of their campaigns. By electing more people like them, Congress can finally listen to the will of the people, not the gun lobby,” Murphy said …”
“… Murphy and Sens. Cory Booker, D-N.J., and Charles Schumer, D-N.Y., have established the “Fund to End Gun Violence,” an effort to “bundle” contributions to U.S. House and Senate candidates who would support gun control bills …”
I can’t find any committee or website with the name so I’m going with the Fund being more antigun astroturf.