AMES, IowaBen Carson has run an unconventional presidential campaign and benefited handsomely. The retired neurosurgeon has never held elected office, but enjoys the support of many Iowans in attendance at the Family Leadership Summit on Saturday.

His most recent book's sales quadrupled in the immediate weeks after launching his presidential campaign, and his personal financial disclosure shows he made more than $4 million from delivering speeches across the country.

Carson continues to give speeches for cash while on the campaign trail, and explained his reasoning for doing so while in Ames, Iowa, this weekend. He said he used to do about 100 or so paid speaking events per year, but only has two or three remaining this year.

"[I] tried to get rid of all of them, but there are a few straggling events," Carson said in response to a question from the Washington Examiner. "Some people have said to me, 'Well, why don't you just cancel those?' Well, what they don't recognize is these people have spent enormous amounts of money, time, and energy getting sponsors, setting tables; frequently this is their annual budget that we're talking about. And for me to just to walk out on them is unethical."

Other presidential candidates have stayed on the paid-speaking circuit while running for president. Former Arkansas Gov. Mike Huckabee collected payment for his speeches during his failed 2008 presidential bid. He wound up with a television show on Fox News after his campaign faltered.

Carson is polling among the top five GOP presidential candidates nationally, and appears poised to appear in the first televised primary debate next month. Carson told reporters the biggest lesson he has learned during the first couple of months on the campaign trail is to avoid making inflammatory statements littered with buzz words.

But Carson also appeared to gain unwanted attention when he declined to say whether Sen. John McCain was a "war hero," in light of Donald Trump's earlier assertion that Trump was a war hero because he was held in captivity. Carson said whether McCain was a war hero "depends on your definition of a war hero," and chose not to provide any explanation. He did say he thought McCain had done some wonderful things.

Carson appears intent on making sure his message does not get lost in the shuffle of comments that others perceive to be controversial, but it appears that he still has some work to do before he takes the debate stage next month.