After 32 people were massacred in 2007 at Virginia Tech, Reid cautioned against a "rush to judgment" about new gun laws.
In 1993, Reid voted against a 10-year ban on assault-style weapons, but ultimately in favor of an omnibus crime bill that included the ban. But in 2004 he voted against an extension of the assault weapons ban, and the law died.
In 2010, top NRA official Wayne LaPierre called Reid "a true champion" of gun rights.
Rory Cooper, spokesman for House Majority Leader Eric Cantor, R-Va., said Monday: "Right now is the moment for prayer and supporting the families of Newtown. There will be time to debate policy in the weeks ahead."
Other Republicans said mental health, not guns, was the problem, and generally stayed away from a debate on gun control.
Rep. Pete Sessions, R-Texas, said: "We recognize those very demented, awkward people commit those crimes. We need to do a better job treating and looking at and finding people who have these problems. That's the issue. We have millions and millions of guns. Guns aren't the problem; sick people are."
Rep. Virginia Foxx, R-N.C., said: "There are just evil people in the world. There's nothing you're going to do to prevent evil from occurring."