In a Republican presidential field where Donald Trump, Ted Cruz, and Ben Carson are topping the polls, Marco Rubio seems like the reasonable, electable choice that the establishment should love.

That may well be true. But among Rubio's policy positions, there's one potential land mine where he's far more conservative than every recent GOP presidential nominee and the vast majority of Americans — his support for banning abortions even in cases of rape and incest.

Indeed, in a speech to the Republican Jewish Coalition on Thursday (flagged by the Washington Examiner's Byron York), rival candidate Lindsey Graham laid out a blunt, stark argument that any Republican with that view is doomed to lose the general election.

"I am pro-life," Graham said. "You can be pro-life and win an election." But, he continued, "if the nominee of the Republican Party will not allow for an exception for rape and incest, they will not win."

Though Graham was crafting a rebuttal to Ted Cruz and didn't mention Rubio by name, the criticism could apply to Rubio as well. Graham argued that if anyone with that position is nominated, the election "will be about rape." He added:

"If you don't think that, then you just don't understand what they [Democrats] will do. It will be about the nominee of the Republican Party telling a woman who's been raped, you gotta carry the child of the rapist. Good luck with that! ... We will lose if that's the position of the nominee of the Republican Party. We will lose young women in droves."

Graham's criticism hasn't been discussed much during the GOP primary so far. But it's a serious substantive disagreement that divides the field in half.

The GOP candidates who support exceptions for rape and incest include Donald Trump, as well as most of the candidates generally considered to have establishment-friendly views: Jeb Bush, John Kasich, Chris Christie, Carly Fiorina, and Graham himself.

But despite generally being described as an establishment-friendly candidate, on this issue Rubio is aligned with the more conservative half of the field — including Ted Cruz, Ben Carson, Mike Huckabee, Rick Santorum, and Rand Paul. (Paul Waldman has a good roundup of the candidates' positions here.)

Rubio made his views on abortion clear during a debate in August

Rubio made his position clear during the first Republican debate back in August. When moderator Megyn Kelly suggested that Rubio supported "a rape and incest exception to abortion bans," Rubio made sure to clarify that actually he supports no such thing (as you can see in the video above).

RUBIO: Well, Megyn, first of all, I’m not sure that that’s a correct assessment of my record. I would go on to add that I believe all human life – KELLY: You don’t favor a rape and incest exception? RUBIO: I have never said that. And I have never advocated that. What I have advocated is that we pass law in this country that says all human life at every stage of its development is worthy of protection. In fact, I think that law already exists. It is called the Constitution of the United States. And let me go further. I believe that every single human being is entitled to the protection of our laws, whether they can vote or not. Whether they can speak or not. Whether they can hire a lawyer or not. Whether they have a birth certificate or not. And I think future generations will look back at this history of our country and call us barbarians for murdering millions of babies who we never gave them a chance to live.

The unusually far-right position Rubio laid out at the time — which Jonathan Allen wrote about for Vox — hasn't yet moved to the forefront of the conversation over the GOP nomination. But it certainly raised the eyebrows of many political insiders and pro-choice activists.

For decades, Republican presidential nominees have said they support banning abortion. But they've also made sure to clarify that they'd support exceptions for victims of rape or incest, or mothers whose lives would be endangered by carrying a pregnancy to term.

Party elites believed that the American electorate would simply never accept banning abortion in those cases too. Indeed, according to one recent poll, 75 percent of Americans think a woman whose pregnancy has been caused by rape should be able to get a legal abortion. As Graham said, the idea that a rape victim should be forced to carry her attacker's child to term is simply repellent to many Americans.

How Rubio might try to pivot to a general election

But Graham is absolutely right that Democrats will seize on this if Rubio is nominated. The party hammered Mitt Romney for being part of a "war on women" in 2012, and GOP Senate candidates like Todd Akin and Richard Mourdock were both hurt badly for making controversial comments about rape.

So in a recent interview with the New Yorker's Evan Osnos, Rubio gave a glimpse into how he might try to soften his views for the general election. See if you can follow it (with bolding added for extra emphasis):

When I asked Rubio about it, he said, somewhat confusingly, "Look, I personally believe that all life is worthy of protection, and therefore I don’t ever require, nor have I ever advocated, that I won’t support a law unless it has exceptions." After some more twists and turns, I sensed that we had reached the line he plans to use in a general election: "My goal is to save as many lives as possible, and I’ll support anything that does that. Even if it has exceptions."

Got that? Rubio's setting the stage for a distinction between his personal views and which policies he'd actually pursue. He's saying that while he doesn't personally support exceptions for rape and incest, he'd be happy to support abortion bans that preserve these exceptions.

From there, he's just a short distance away from the even more general-election-friendly position that would go something like this: "It's clear the American people want exceptions for rape and incest. So while my own personal views are different, I won't try to pursue policies to that end."

Rubio could also simply flip-flop on the issue, like Bob Dole did in December 1995. But as former Obama strategist David Axelrod told Osnos in the New Yorker piece, "Presidential races are defined by moments. Maybe he will try to amend that position, but in the age of video it’s hard to extinguish a declarative statement like that."

This is what worries Graham. "If you're gonna tell a woman who's been raped that she has to carry the child of the rapist, you're losing most Americans," he said. "How do you get a pro-choice person to vote for you?"