Carson gains steam in Iowa

Ben Carson has moved up to the top spot in Iowa, a poll of likely Republican caucus-goers has found.

The retired neurosurgeon leads the Republican field with 28 percent, while Donald Trump has fallen to 20 percent, according to a new Quinnipiac University poll. A September poll had Trump at 27 percent and Carson at 21 percent.

The poll also showed a surging Marco Rubio. The Florida senator comes in third with 13 percent, after getting only 5 percent in last month's poll.

After Rubio comes Kentucky Sen. Rand Paul (6 percent), former Hewlett-Packard CEO Carly Fiorina (5 percent) and former Florida Gov. Jeb Bush (5 percent). All other candidates garner under 3 precent of support from likely Iowa Republican caucus participants.