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"For me, giving to charity, I've always viewed that the things that I do in my life contribute to making lives better. That what I've done."

Gary Johnson estimated his effective tax rate to be around 20 percent.

Johnson also said he does not expect 2012 Republican presidential nominee Mitt Romney to endorse him "for all sorts of reasons."

"I'm not expecting it," he said. "So given my expectations, everything's a bonus."

Johnson has been aiming to get on the debate stage by getting a minimum of 15 points in the national polls by September. He has been polling at around 8 percent of late.