Colorado had already passed legislation requiring background checks for all private gun sales, and a ban on large magazine rounds.
And it finances the National Rifle Association to oppose even mild gun safety legislation like background checks on gun buyers and stiffer penalties for gun trafficking.
That legislation requires background checks on buyers in private gun sales, and limits an assault rifle's magazine to fifteen rounds.
4.41pm BST More from the Senate announcement of bipartisan legislation requiring background checks on all firearm purchases: "Truly the events at Newtown changed us all," Senator Manchin said.
Federal legislation requiring background checks and a 21-day waiting period for the purchase of a handgun could have prevented the tragedy at City Tech.
Gabrielle Giffords, a former congresswoman for Arizona, held a news conference in Tucson to urge Senators John McCain and Jeff Flake to support legislation requiring background checks for every gun purchase.
In January, State Representative Miguel P. Garcia, a Democrat from Albuquerque, proposed legislation requiring background checks for purchases of firearms made at gun shows and through private sales — both currently unregulated in New Mexico.
But despite broader Republican support for an immigration overhaul, the inability of Congress to pass modest gun legislation involving background checks is a warning for the immigration bill's journey.
Almost immediately after the murders in Newtown, gun control advocates and the Democratic leadership in the Senate decided that legislation strengthening background checks for gun purchases was their best avenue for success.
Already, two N.R.A. allies — Senators Patrick J. Toomey, Republican of Pennsylvania, and Joe Manchin III, Democrat of West Virginia — have broken with Mr. LaPierre to sponsor legislation extending background checks, which a bipartisan group of senators has embraced.
