Ben Carson has pulled ahead of Donald Trump in the latest Iowa caucus poll, bumping the billionaire out of the top spot in the state for the first time since early August. 

The Quinnipiac University survey showed the retired neurosurgeon leading Trump 28-20 percent among likely GOP caucus-goers. 

Both political outsiders have been dominating the polls since the summer, both nationally and in key states. But Carson had been trailing Trump in Iowa until now. 

"It's Ben Carson's turn in the spotlight," Peter A. Brown, assistant director of the Quinnipiac University Poll, said in a statement. 

The findings come ahead of the third Republican presidential debate, set for next week. In the past two bouts, Carson and Trump largely have avoided sparring. Though both outsider candidates have a reputation for controversial remarks, their political styles are very different -- with the former soft-spoken and genial on the campaign trail, in contrast with Trump's confrontational approach. 

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The Iowa poll showed Carson leading among women compared with Trump, 33-13 percent, while they were almost evenly split among men. 

Carson also led the field in the eyes of Republican caucus-goers on the question of who they find honest and trustworthy. 

The survey also showed Florida Sen. Marco Rubio in third place with 13 percent, followed by Texas Sen. Ted Cruz with 10 percent. The Iowa survey of 574 likely Iowa Republican caucus-goers was taken Oct. 14-20. It had a margin of error of 4.1 percentage points. 

Trump continues to lead nationally by several points in an average of polling, according to RealClearPolitics. 

But Iowa isn't the only state where Carson is rising. A Wisconsin Public Radio survey showed Carson leading in the state with 20 percent, with Trump and Rubio at 18 percent, among probable and definite primary voters.