WASHINGTON -- Gun-rights defenders and manufacturers of the popular AR-15 semiautomatic rifle -- the weapon used in the Newtown, Conn., killings -- girded for the worst Tuesday as gun control moved to the forefront of the legislative agenda in the nation's capital and retailers pulled the weapon from stores and websites.Republicans and Democrats were in rare lockstep as prominent figures in each party called for a special commission to look into the shootings at Sandy Hook Elementary School and recommend changes in gun laws and the nation's mental health system.Retailers were either removing high-powered weapons from their sales floors or pulling down online information on the weapons used in the mass killing and in shootings this month at an Oregon mall and this summer in Aurora, Colo.The National Rifle Association, the nation's largest gun lobby, broke its silence Tuesday, saying its members are "shocked, saddened and heartbroken" by the "horrific and senseless murders."The NRA, which plans a news conference Friday, said it is "prepared to offer meaningful contributions" to prevent another such massacre.President Barack Obama and Vice President Joe Biden have huddled with Cabinet members and senior staffers this week to begin forging a more formal response to the Sandy Hook shootings.White House spokesman Jay Carney said Obama is "actively supportive" of legislation reintroduced by Sen. Dianne Feinstein, D-Calif.Feinstein hopes to revive an assault weapons ban that expired in 2004, and Carney said Obama also supports ending a loophole that allows Americans to skirt background checks by buying assault weapons at gun shows."And there are other elements of gun legislation that he could support," Carney said, adding that the president is "interested in looking" at legislation on high-capacity magazines.One reason that last week's killing spree was so deadly is that gunman Adam Lanza had large-capacity magazines and could fire multiple times before having to reload.Makers of the AR-15 wondered whether they might soon be legislated into oblivion."Our sole business being the assault rifle, it is a concern that it will literally put us out of business," said Ken Rinkor, vice president of Tactical Arms Manufacturer Inc. in Huntersville, N.C."That is not for us to determine. If the general public decides to vote the way of banning assault rifles, then they can certainly do so."The family-owned company near Charlotte is a specialty manufacturer of the AR-15, advertising on its website that "the same AR15 M4 used by the U.S. Army can be your home defense weapon of choice."The company sells mostly to law enforcement, Rinkor said.While he fears a ban on the rifles, Rinkor supports calls for outlawing sales of high-capacity magazines."Frankly, I think there's no need for anybody to have such ... magazines, 20 or 30 rounds. It makes no sense at all," he said.Gun show loopholeCarney also said Obama supports closing a loophole that limits scrutiny of weapons sales at gun shows. This was a new level of detail about the president's goals for gun legislation."People have talked about restricting high-capacity ammunition clips, for example, and that is something that he would certainly be interested in looking at."Carney's comments came after high-profile shifts by several Democrats who have been friendly to the gun lobby.On Monday, Sens. Joe Manchin of West Virginia and Mark Warner of Virginia said they would be open to reinstating the assault weapons ban. There also were new calls to deal with gun control from three incoming senators who had been backed strongly by the NRA.