With the exception of Nebraska, every state that Carson visits to promote his book votes by March 15. Carson, already a best-selling author from previous books, is drawing big crowds and free media. And the tour helps him boost his name identification against Donald Trump, who currently leads GOP polls, in part because his name ID is so strong.

“If he does it right, it can just enhance the campaign,” said former House Speaker Newt Gingrich, who ran a book tour while campaigning in the last presidential cycle, a move that didn’t appear to hurt him at the time, though he ultimately was defeated.

The key, he said, is to structure book stops as an extension of the campaign: “You’ve got to put them together so they reinforce each other. Don’t go to a great book town [if it doesn’t help the campaign,]” Gingrich said.