Outside expenditure numbers from the Center for Responsive Politics include spending by the NRA and affiliates to influence elections in 2010 and 2012. Does not include direct contributions to candidates. Some amounts are too small to show on the graphic.

   Pat Toomey 2010 - $901,914 contributed, $600,432 spent against opponent.
   Bob Casey - No contributions
   Jim Gerlach - 2012 $1,357 contributed, 2010 $3,722 contributed.
   Pat Meehan - 2012 $893 contributed, 2010 $25,465 contributed.
   Mike Fitzpatrick - 2012 $23,824 contributed.
       
 
   

The conversation about gun control keeps shifting in the wake of the mass shootings in a Newtown, Conn., elementary school.

On Wednesday, President Barack Obama for the first time in his tenure delivered a call for new legislation.

"If there is even one thing we can do to prevent any of these events, we have a deep obligation, all of us, to try," he said.

"It's encouraging," he added, "that people of all different backgrounds and beliefs and political persuasions have been willing to challenge assumptions and change long-held positions."

U.S. Sen. Bob Casey of Pennsylvania could be the poster child for that conversion.

Casey, a Democrat with a pro-gun reputation, has opposed enacting new gun-control measures ... until now. Casey said the massacre of first-graders in school by a man armed with an assault weapon and hundreds of bullets shook him in ways that other shootings had not.

"I'm haunted by the fact that he could have killed hundreds of children. Not only the 20 children who lost their lives," he said. "If you're not haunted by that and if that doesn't cause you to think ... especially as a legislator who has a vote."

A new CBS News poll shows the majority of Americans now support stricter gun laws.

Congress most likely will consider an assault weapons ban and a limit on very large magazines of bullets.

"I think this was seismic," Casey said. He would vote for both measures today.

But what about the Pennsylvania's other U.S. senator, Pat Toomey?

Toomey notably said on the campaign trail in 2010 that, "My idea of gun control is a steady aim."

The NRA backed the Republican Toomey strongly that year, as NRA affiliates spent a little over $8 million on outside expenditures in support of federal candidates in 2010. That's money that doesn't go straight to the campaign. Think PAC-funded TV ads, etc.

More than $900,000 of that went to support Toomey, more than any other Senate candidate that year. In addition, the NRA affiliates spent $600,000 to help defeat his opponent, Democrat Joe Sestak. In all, $1.5 million went into  Toomey's race.

Toomey's office declined to offer a statement on how this support affected his position.

Asked whether the events had changed his stance on gun control, he issued this statement:

"I was horrified to learn about the mass murder in Newton, Conn., and my thoughts and prayers are with the victims and their families. In response, we need to come together as a nation, carefully reflect on what happened, and have a thoughtful dialogue on how we can improve public safety and protect our children from such violence. Among other things, we need to implement more effective methods of identifying and protecting ourselves from dangerous and mentally deranged individuals who seek to carry out such atrocities."

The National Rifle Association has scheduled a press conference Friday to respond to the Newtown shootings.