Image copyright Getty Images

Retired neurosurgeon Ben Carson, one of the current frontrunners for the Republican presidential nomination, wants to make abortion illegal in all instances, including cases of rape and incest.

He told an NBC News interviewer on Sunday that he's a "reasonable person", however, and he'd listen if someone can come up with a "reasonable explanation for why they would like to kill a baby". Women, however, should not look at their foetus as "the enemy".

To illustrate his point, Mr Carson - whose understated yet forceful condemnations of liberal orthodoxy made him a darling on the conservative lecture circuit before he launched his presidential bid - offered an analogy that compared women seeking abortions to slaveholders.

"I know that's one of those words you're not supposed to say, but I'm saying it," Mr Carson began. "During slavery, a lot of slave-owners thought they had the right to do whatever they wanted to that slave, anything that they chose. And what if the abolitionists had said, 'I don't believe in slavery, but you guys do whatever you want'? Where would we be?"

Mr Carson has made a habit of saying what he's "not supposed to say" and then deriding the subsequent firestorm as attacks from "politically correct" critics.

The retired doctor has said President Barack Obama's healthcare reform was "the worst thing" since slavery and that the US government is acting like Nazi Germany. He asserted that being gay is a choice, Muslims aren't qualified to seek the US presidency, the Holocaust could have been prevented if persecuted Europeans owned more guns and - just a few days ago - that the US government should cut off funding to universities that are found to exhibit "extreme political bias".

Mr Carson's comments on abortion have set off yet another cycle of outrage from the left - a reaction that he will likely wear as a badge of honour.

"Carson's comments are part of a larger disinformation campaign by Christian fundamentalists and other elements of the American right in which examples from the United States' slave regime are used to delegitimise women's full equality and freedom," writes Salon's Chauncey Devega.

Image copyright Getty Images Image caption Ben Carson is attracting a devoted following despite controversial statements

The Washington Post's Jonathan Capehart writes: "Carson is a crackpot who should get nowhere near the White House, let alone the presidential nomination of a major political party. His incendiary and ignorant comments - not political correctness, not racism - are the cause of the 'relentless attacks' on him."

At one point, according to the New York Times, Mr Carson's political team was concerned about their candidate's propensity to make off-the-cuff statements that provoked outrage. In the end, however, they decided to "let Carson be Carson" - and the results have validated their instincts so far.

Much like fellow Republican frontrunner Donald Trump before him, Mr Carson has soared in public opinion polls of likely Republican primary voters despite controversial statements that would sink more traditional politicians.

In recent surveys of Iowa, the state where voters will first help select presidential nominees, Mr Carson has tied or even taken the lead from Mr Trump. In a Monmouth University poll released Monday, Mr Carson is backed by 32%, 14 points over second-place Trump.

This development has prompted the New York billionaire to begin targeting Mr Carson.

He remarked this weekend that the soft-spoken candidate is "super low on energy". He told a CNN interviewer that Mr Carson wouldn't be able to make deals with nations like Japan and China.

He tweeted that Mr Carson wasn't a job-creator and would abolish, the government-run healthcare system for the elderly. He also raised questions about Mr Carson's particular brand of evangelical Christianity.

Image copyright Getty Images Image caption Donald Trump says Ben Carson is "super low on energy"

"I'm Presbyterian," he said during a campaign stop in Florida. "Boy, that's down the middle of the road. I mean, Seventh-day Adventist, I don't know about. I just don't know about."

In the same interview where he made his abortion remarks, Mr Carson said the he wouldn't get in the "mud pit" to respond to attacks, but noted that he had the energy to conduct 20-hour surgeries when he was a practising physician.

As the Washington Examiner's Byron York points out, Mr Carson presents a tricky opponent for the other Republican presidential hopefuls. While Mr Trump has decided to go on the attack, others have been reluctant to follow suit by criticising the physician's lack of governing experience.

Veteran political operatives, he writes, are concerned that Mr Carson's high popularity in polls means any attack will backfire.

"Republican candidates have a Ben Carson problem," York writes. "He's ahead of most of them. They want to win. But how do they defeat him without offending the voters who admire him? No one has yet found the answer."

With just over three months before Iowans head to the polls and other states quickly follow suit, the clock is ticking.

Candidates in (and out of) the Republican presidential field