Michael R. Bloomberg, making his first major political investment since leaving office, plans to spend $50 million this year building a nationwide grass-roots network to motivate voters who feel strongly about curbing gun violence, an organization he hopes can eventually outmuscle the National Rifle Association.

Mr. Bloomberg, the former mayor of New York, said gun control advocates need to learn from the N.R.A. and punish those politicians who fail to support their agenda — even Democrats whose positions otherwise align with his own.

“They say, ‘We don’t care. We’re going to go after you,’ ” he said of the N.R.A. “ ‘If you don’t vote with us we’re going to go after your kids and your grandkids and your great-grandkids. And we’re never going to stop.’ ”

He added: “We’ve got to make them afraid of us.”…

But if he senses that he may not have as much time left as he would like, he has little doubt about what would await him at a Judgment Day. Pointing to his work on gun safety, obesity and smoking cessation, he said with a grin: “I am telling you if there is a God, when I get to heaven I’m not stopping to be interviewed. I am heading straight in. I have earned my place in heaven. It’s not even close.”