Ben Carson is winning over Iowa

Retired neurosurgeon Ben Carson has emerged as a leading Republican presidential candidate in Iowa and is closing in on front-runner Donald Trump in the state that hosts the first 2016 nomination balloting contest.

The latest Bloomberg Politics/Des Moines Register Iowa Poll shows Trump with the support of 23 percent of likely Republican caucus participants, followed by Carson at 18 percent. When first and second choices are combined, Carson is tied with Trump.

Although he isn't generating the headlines enjoyed by Trump, Carson has quietly built a dedicated network of supporters in Iowa. In the past month, he also aired more ads than any other presidential candidate in Iowa. Carson has the highest favorability rating among Republican candidates, with 79 percent of likely GOP caucusgoers seeing him positively.

The latest Iowa Poll shows Trump is rated favorably by 61 percent and unfavorably by 35 percent.