The statistics are staggering, the stories heartbreaking, yet there is little chance that any amount of bloodshed will lead to stiffer gun controls in the United States in the foreseeable future.

"It's not something that any politician thinks is winnable," said Kristin Goss, a politics professor at Duke University and author of "Disarmed: The Missing Movement for Gun Control in America."

Five years after the worst school shooting in US history left 32 people dead at Virginia Tech, another high profile slaying has raised fears that new self-defense laws allow armed vigilantes to kill with impunity.

Florida authorities initially refused to charge a neighborhood watch volunteer for killing a black teenager even though a 911 operator instructed George Zimmerman not to follow the boy and instead to wait for police, after he first called to report a guy "up to no good."

That's because Florida -- like 24 other US states -- has a "Stand Your Ground" law that grants immunity from prosecution if people use deadly force because they felt threatened.

Zimmerman said Trayvon Martin, 17, attacked him and under Florida law, he had no duty to attempt to safely retreat before firing his gun. The US constitution guarantees the right to bear arms, and individual states can regulate the right.

The Trayvon Martin case sparked protests across the country after Martin's family, lawyers and civil rights leaders alleged the hoodie-wearing teen -- who was on his way home after buying iced tea and a pack of Skittles -- was a victim of racial profiling.

It also highlighted the dramatic weakening of gun controls, as well as the role of the National Rifle Association (NRA) and a once little-known conservative think-tank that drafted Stand Your Ground and other gun rights law and pushed them through state legislatures.

Statistics on gun victims -- 11,500 homicides, 554 accidental deaths and 45,000 non-fatal assaults in 2009 -- are brushed aside with the adages "guns don't kill people, people kill people" and "bad guys can't be the only ones packing heat."

"The NRA's greatest success has been divorcing not just their rhetoric but their legislative agenda from the real world," said Josh Sugarmann, director of the Violence Policy Center, which advocates for gun control.

"One of the most striking things we're seeing coming out of the Trayvon Martin case is for the first time in many, many years people are saying 'what actually happened?'"

Stand Your Ground laws that have granted immunity to people who shot robbers after chasing them for several blocks and drug dealers who killed rival gang members are relatively new, as is the pervasiveness of guns, which can now be brought even into churches, schools and bars in many states.

Illinois is the only US state that still bans concealed weapons, down from 19 in 1981.

The number of states with permissive gun laws -- which typically only prohibit felons, drug addicts, children and the mentally ill from carrying concealed weapons -- expanded from three to 39 in the past 30 years.

It's a disastrous combination that encourages people to engage in unnecessary violence, said former Miami police chief John Timoney.

"You want to have the ability to judge every case individually," said Timoney, who fought to block the passage of the nation's first Stand Your Ground law before it was implemented in Florida in 2006.

"You don't want to have some law letting people say I'm going to kill my wife and pretend I thought she was a burglar."

Zimmerman was eventually charged with murder on April 11 after a special prosecutor was appointed to investigate the February 26 shooting. Florida's governor has set up a task force to review the Stand Your Ground law.

But experts say there's only a slim chance that some states will repeal their Stand Your Ground laws and almost none that any attempt will be made to tighten gun controls.

"Once you have a law in place, it's hard to change it," said Clyde Wilcox, a professor at Georgetown University who specializes in public opinion and controversial issues.

"At the moment, the Democrats and liberals are a little afraid to push on this and are afraid it'll backfire in national politics."

Many Democrats say Al Gore lost the 2000 presidential election because of his focus on gun control and they fear the issue could harm President Barack Obama's reelection bid in November.

One reason for the NRA's success is its ability to frame the debate as a fight for freedom, the American way and the right to defend yourself, said Robert Spitzer, author of "The Politics of Gun Control."

"There is a long ethos of individualism, the idea that citizens really need to take care of their own problems, not rely on the government," said Spitzer, a professor at State University of New York at Cortland.

"That feeling has also contributed to the idea that the citizen with the gun is somehow a bulwark of liberty."

Mass shootings that once led people to call for tougher gun controls are now used by gun advocates as a reason to let students bring guns onto college campuses.

Even though violent crime rates are actually down sharply, it's a convincing argument for many.

"People who own guns feel empowered," Spitzer said. "That's surely why George Zimmerman had a handgun with him."