Think the gender gap was big in 2012? Just wait for 2016.

Since Donald Trump announced his candidacy last year, he has insulted the appearance of former GOP rival Carly Fiorina; made implicit references to Megyn Kelly's menstrual cycle; gone after Ted Cruz's wife, Heidi; and suggested Hillary Clinton wouldn't get "5 percent" in the polls if she weren't a woman.

Now that he's the presumptive GOP nominee, Republican women are faced with a difficult choice. Do they fall in line for Trump, despite their distaste for his rhetoric? Do they back Hillary Clinton, whose policies they disagree with (sometimes vehemently)? Or do they stay home and sit out the race entirely?

"There's so many conservative women out there right now who I think are grappling with this issue," said Sabrina Schaeffer, executive director of the Independent Women's Forum.

With Election Day still six months away, operatives acknowledge that things aren't set in stone. But in interviews with half a dozen Republican female operatives, most expressed to CBS News their strong concern that Trump's rhetoric will cause a huge gender gap and sink the GOP among women voters, an integral demographic to winning the White House in November.

The numbers are stark: back in March, 47 percent of Republican women primary voters said in an NBC/Wall Street Journal poll that they could not imagine themselves voting for Trump — far higher than for any of the other GOP hopefuls. And according to the last CBS News national GOP primary poll, released in mid-April, just 44 percent of Republican women viewed Trump favorably. The numbers are even more abysmal among women overall.

"This is going to be a choice between kind of two poison pills: it'll either be Hillary Clinton or Donald Trump," said Mindy Finn, a GOP strategist who leads the independent group Empowered Women.

Trump's rhetoric on women has been a tool his detractors have worked to use against him in the primary, too. Back in March, the anti-Trump group Our Principles PAC ran what's perhaps the most memorable anti-Trump ad of the cycle, in which women read the candidate's actual past comments on women out loud.

"'Bimbo … Dog … Fat pig" the women read out in the ad. "Real quotes from Donald Trump about women."

GOP operatives acknowledge those words won't go away easily, and that Trump's rhetoric will play endlessly in Democratic campaign ads. Even if they agree with him on policy, they said, it's his personality and tone that makes him so unpalatable.

"It's harder for women than for men to get over that character piece," Schaeffer said. "The brazenness with which Trump has often talked about women is perhaps a step too far."

She added that Republican women's groups, including IWF, have worked hard in recent years to convince women voters that Republicans want to talk to them — and worried that Trump would effectively undo all of those efforts.

Liz Mair, a GOP operative who's been a vocal part of the #NeverTrump movement, put it more bluntly: "He acts like an overgrown frat boy."

"It's going to take a lot for Republican women to feel warm and fuzzy about Hillary Clinton. But Trump is somehow doing that," she said. "The vast majority of women out there have had a Trump-like guy hit on them at some point, and most have said, 'No way am I dating that guy.'"

The threat to Republicans was evident after the Northeastern primaries in late April, when Trump's team had been saying he would be more presidential — but he still railed on Clinton's use of the "woman card," telling supporters at an election night event that if Clinton "were a man, I don't think she'd get 5 percent of the vote."

Clinton's campaign quickly seized on Trump's comments, sending out a fundraising plea to supporters and selling a "woman card" and other related merchandise in its online store. The move brought in $2.4 million from 118,000 donors in just three days, according to the Clinton campaign, 40 percent of whom were new donors.

In other words, it could make 2012 — in which Democrats trumpeted a GOP "war on women" to help sway swing-state suburban women away from Republican nominee Mitt Romney — look tame by comparison. Finn said Clinton can and will make her pitch to more moderate Republican women in swing-state suburbs, and that unless Trump changes his tune she'll likely make gains among the demographic.

What's still unclear at this point is whether any GOP women's groups will actively oppose Trump, or just sit the race out entirely. A spokeswoman for Susan B. Anthony List, the pro-life women's group that was highly critical of Trump during the primary process, told CBS News the group will continue going after Clinton in the general election but did not say whether the group will explicitly boost Trump.

Back in January, SBA List put out a letter signed by top pro-life female activists saying Trump "has impugned the dignity of women," naming Kelly and Fiorina specifically. "As women, we are disgusted by Mr. Trump's treatment of individuals, women, in particular," the letter said.

"From our perspective we're in a general election situation now," SBA List's Mallory Quigley said. "Donald Trump, the presumptive nominee, he's made very specific pro-life commitments and if elected we're going to look for those fidelity to those commitments."

Quigley added: "We know exactly what Hillary Clinton will do, and we do not want to see Hillary Clinton in the White House for sure."

CBS News' Will Rahn contributed to this story.