Ben Carson. REUTERS/Mike Stone Retired neurosurgeon Ben Carson just achieved a milestone in the Republican presidential primary: edging front-runner Donald Trump in a notable poll.

Quinnipiac University released a new Iowa survey on Thursday that found Carson leading Trump 28% to 20% among likely caucus-goers.

Trump has led almost every national and state-based poll since he surged to the top of the crowded field over the summer, and he has continued to hold decisive leads in several new polls out this week.

But Carson has been nipping at his heels.

"It's Ben Carson's turn in the spotlight," Quinnipiac pollster Peter Brown said in a statement on the Iowa results.

"As they've been pondering for six months, many in the political world still are trying to understand Carson's appeal and how someone who seems to be operating outside the traditional news media/political environment is doing so well among the most conservative GOP voters."

Brown cited Carson's support among women as contributing to his strength in the survey.

Carson addressed that topic later in the day during an interview with by WABC Radio host Rita Cosby.

"Probably, I suspect because when I talk about issues, and I talk about things, I really don't distinguish. And I think everybody knows that I'm going to be totally fair in everything I do. I hope that's what it is," Carson said.

After Cosby asked if Trump's various campaign-trail controversies contributed to his edge among women, Carson appeared to agree.

"I never presume to speak for anybody else. But certainly, there have been things that I think people might take offense at," he said.

Donald Trump. AP Photo/Charlie Neibergall

Brown also pointed to Carson's support among Iowa's "sizeable white, evangelical Christian community," where he led Trump 36% to 17%.

Historically, socially conservative and openly religious candidates have done well in Iowa, the first caucus state on the 2016 slate.

Former Sen. Rick Santorum (R-Pennsylvania), a devout Catholic, won the state in 2012. Former Arkansas Gov. Mike Huckabee (R), a Southern Baptist minister who is running again this year, won the state in 2008. Carson attends a Seventh-day Adventist church and frequently invokes his faith on the campaign trail.

And Carson is widely liked among Republican voters, according to the Quinnipiac poll and others.

"Those who know Carson seem to like him," Brown added. "He has an almost unheard of 84-10 percent favorability rating among likely Republican caucus-goers, compared to Trump's 53-43 percent rating. To borrow the line from Madison Avenue, 'Almost no one doesn't like Ben Carson.'"

After Carson and Trump, Sen. Marco Rubio (R-Florida) grabbed the third-place spot in the poll, with 13% support among likely caucus-goers. Sen. Ted Cruz (R-Texas) followed him with 10%. Sen. Rand Paul (R-Kentucky) had 6%, while former Florida Gov. Jeb Bush (R) and former Hewlett-Packard CEO Carly Fiorina both tied at 5%.