Still, Perry may have undermined his effort to focus on his policy ideas when he said in a CNBC interview today he would continue to question the authenticity of President Barack Obama's birth certificate, an issue raised by some social conservatives who say Obama isn't eligible to be president. In April, Obama released his birth certificate, issued by the state of Hawaii, which shows his birthplace as Honolulu.

"It's a good issue to keep alive," Perry told CNBC. "It's fun to poke him a little bit," he said of Obama, adding that while the issue is a "great distraction," he is "not distracted by it."

Differences With Romney

Perry's economic plan sets him apart from Mitt Romney, the former Massachusetts governor and second-time presidential candidate who is leading in Republican primary polls. Romney last month released a 59-point, 160-page jobs proposal that keeps the existing tax system while extending income tax cuts now set to expire and reducing investment taxes and the corporate rate.

Perry invited people to look at his own plan and said, "It is not the length of the novel War and Peace, by the way." Other candidates, he said, were offering "microwave plans with warmed-over reforms based on the current ingredients."

Obama's campaign criticized both men's plans as extreme ideas that wouldn't create jobs. Romney's and Perry's proposals "would shift a greater share of taxes away from large corporations and the wealthiest onto the backs of the middle class," Ben LaBolt, the campaign's press secretary, said in a statement. "The belief that middle class Americans will benefit if we just give another special break to those at the top was long ago discredited."

Less Progressive

A flat tax -- even an optional one -- by definition would be less progressive than the current system, where the top individual income and corporate tax rates are 35 percent. The highest earners currently pay a higher percentage of taxes while those who earn less owe a lower percentage, with the lowest earners paying no income taxes.

In the CNBC interview, Perry said he doesn't believe the country should have a progressive tax system and isn't worried about being accused of giving massive tax breaks to the wealthy.

"When the federal government tries to take too much, they end up hurting the very people they supposedly seek to help: the working class," Perry said in his speech. "We need tax policy that embraces the world as it is, not as some liberal ideologue wishes it to be."