The calls for President Obama to take on gun control began immediately after the deadly shooting at a Connecticut elementary school, but history has shown that changing firearm laws that have deeply divided Americans will prove extremely difficult.

Like similar massacres at Columbine High School, Virginia Tech and a Colorado movie theater, gun-control advocates insist the tragedy at Sandy Hook Elementary in Newtown, Conn., will prompt action in the halls of Congress and give Obama the political cover to push stringent anti-gun laws.

The difference this time, experts said, is the national reaction to the brutal slaying of 20 first graders.

"The Sandy Hook massacre may be a turning point in America's gun debate; to see 20 children mercilessly slaughtered in a school room, that may be too much for Americans to bear," said Adam Winkler, a law professor at the University of California, Los Angeles, and author of the book, "Gunfight."

But he added, "If the political environment isn't fertile ground for gun control, then nothing is going to happen."

The White House announced late Saturday that Obama will appear at an interfaith vigil Sunday at 7 p.m. in Newtown.

Liberals have accused Republicans of being held hostage to the interests of the powerful gun lobby. But evidence shows that the public has mixed feelings about how its leaders should regulate firearms.

A survey conducted by the Pew Research Center -- after the shooting at a movie theater in Aurora, Colo., in July -- found that, despite public outrage, attitudes about gun ownership remained the same in polls taken before and after the event. That pattern was also seen by the researchers after other high profile mass killings like the one at Virginia Tech. "Recent shootings had little impact on gun control views," Pew found.

That split has fueled Obama's reluctance to significantly pursue gun restrictions. The president called for reforms Saturday but didn't specify any action, hoping to keep the focus on the victims and their families.

"Any of these neighborhoods could be our own," the president said in his weekly radio address. "So we have to come together and take meaningful action to prevent more tragedies like this, regardless of the politics."

Some congressional Democrats, however, said a national conversation on gun control can't wait.

"If now is not the time to have a serious discussion about gun control and the epidemic of gun violence plaguing our society, I don't know when is," Rep. Jerrold Nadler, D-N.Y., said. "How many more Columbines and Newtowns must we live through?"

Gun-control advocates say the new Congress will likely consider at least two proposals when it convenes in January. One would revive the assault weapons ban and include additional types of weapons. Another would expand the use of criminal background checks on gun buyers. About 40 percent of current gun sales, including gun-show sales, don't require background checks.

But many of the reforms being pushed by gun-control advocates were already on the books in Connecticut, home to some of the strictest gun laws in the nation. And a gunman in Norway last year blew up a government building and fired off rounds into a youth camp, killing 77 people, in a country with some of the most rigid gun restrictions in the world.

With Obama's final election behind him, gun-rights supporters had been gearing up for a fight with the White House even before the mass shooting in Connecticut. The National Rifle Association on Saturday said it would not comment on the Connecticut shooting "until the facts are thoroughly known." But in a recent interview, a spokesman for the organization told The Washington Examiner, "We've told people to plan for gun bans and a Supreme Court stacked with anti-gun judges."