Opinion polls in Iowa indicate that Donald Trump is beginning to lose some ground in his campaign to claim the Republican Presidential nomination. 

Trump has been knocked off the top spot by Ben Carson, the retired neurosurgeon who, on the surface at least, seems to be at the other end of the scale to Trump when it comes to personality. 

According to the latest Quinnipiac University poll of Iowa Republicans as reported by CNN, Carson has opened up a lead of 8 percentage points on Trump, with 28% of people claiming they'd support him over the 20% who are backing Trump. 

This jump in the polls has been attributed to growing support from female voters as well as evangelical Christians. 

Image: Andrew Harnik / AP/Press Association Images

Similar to Trump, Carson has been hitting the headlines for the wrong reasons during his campaign too, including his remark that he "would not advocate that we put a Muslim in charge of this nation". However, he hasn't backed down from those comments, saying instead that they were blown out of proportion by the media and that "American people, the majority of them, agree and they understand exactly what I am saying". 

Speaking on CNN, Trump seemed unfazed by the loss of his lead in Iowa, and refused to rule out the possibility of a joint Trump/Carson ticket, saying that he and Carson have a good relationship and "stranger things have happened". 

However, as the site fivethirtyeight points out, with a number of interesting charts to back up their findings, Trump's campaign is in more trouble than simply losing the lead in an opinion poll, as he is badly struggling when it comes to getting endorsements from within the Republican party.

As Aaron Bycoffe highlights in the piece, the process of securing endorsements from influential figures in the party, be they senators or governors, is a crucial part of the the campaign and is often referred to as the "invisible primary".

When it comes to that particular race, Jeb Bush is easily leading the way over both Carson and Trump.