Casey: Gun vote could impact Republicans in midterm election

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"I think there is going to be some impact," Casey told MSNBC. "But I think what we're going to see now, is a change in political dynamics in an electoral sense. And that might have as much impact as anything any kind of emotion, or stirring of the heart that came from the tragedy itself."

The Pennsylvania Democrat predicted that "the next election cycle will create a dynamic we've never seen" in which advocates of gun control would counter the National Rifle Association's traditional influence.

"You won't have a one-sided argument," Casey said. "You're going to have funded television ads. You're going to have funded campaigns against candidates, and that will change the dynamic as much as the tragedy."

Jon Carson, the executive director of Organizing for Action — the advocacy group built from President Obama's reelection campaign — said last week that the organization would target senators, including Democrats, who opposed the gun control legislation. Former Rep. Gabrielle Giffords (D-Ariz.) and New York City Mayor Michael Bloomberg have also organized pro-gun control political action committees that plan to spend heavily before the midterms.

Casey said that he changed his mind on gun control following the Newtown, Conn., tragedy, in which 20 schoolchildren and six educators died.

"I think every one of us has to ask kind of a basic question," Casey said. "When you look at yourself in the mirror, and you have a vote in the United States Senate, you have to say am I doing everything I can to substantially reduce the likelihood that this will happen again?"

But he added that he saw it as unlikely that others would have a similar change of heart until they saw an electoral incentive.

"I think the dynamic is going to change. You're in one lane, or the other. I think to get more people to cross lanes, we've got to have an election cycle," Casey said.