US Republican presidential hopeful Ben Carson has dropped out of the race for the White House after a series of disappointing primary results. The 64-year-old retired neurosurgeon topped opinion polls towards the end of 2015 but lost popularity after a string of poor debate performances. He ran an expensive presidential campaign in which he raised more money than any other Republican candidate.

"Even though I might be leaving the campaign trail, you know there's a lot of people who love me. They just won't vote for me," Carson was quoted as saying by CNN. "But it's OK. It's not a problem. I will still continue to be heavily involved in trying to save our nation.

"I did the math. I looked at the delegate counts... and I realised it simply wasn't going to happen. And if that's the case, then I simply don't want to interfere with the process."

There are now just four Republicans left in the race for the White House, down from the original 17.

Trump backing

Carson's decision to withdraw from the race was widely expected after a poor showing in the Super Tuesday primaries. On 2 March, he said he did not see "a political path forward". The retired neurosurgeon said he would not endorse any of the remaining candidates, but spoke favourably of current front-runner Donald Trump.

Donald Trump
Donald Trump remains the favourite to land the Republican presidential nominationReuters

"People who think Donald Trump would be the worst thing that ever happened... you make a really big mistake trying to thwart the will of the people," he stated. "He's smart enough to know that he cannot have a successful presidency with some of the things that he's talking about, so he would appoint people who were very, very good and very, very smart and he would largely stay out of their way."

Real estate mogul Trump, 69, has won primaries and caucuses in 10 states so far and is leading the race for the Republican presidential nomination.