Views that sexual harassment charges against Herman Cain are a “serious matter” have soared since two of his accusers went public, his unfavorable ratings have jumped and a plurality of Americans — especially women — are inclined to believe the allegations.

The findings of the latest ABC News/Washington Post poll mark a dramatic challenge to Cain’s candidacy. Results a week and a half ago found him showing initial resilience against news of the charges. But as two women have come forward, doubts have risen. Americans by an 11-point margin, 44 percent to 33 percent, say they’re inclined to believe Cain’s accusers over his denials.

The most dramatic change is a jump among potential Republican voters who see the matter as a serious one. Thirty-nine percent said so the week before last; that’s rocketed to 61 percent now. It inches slightly higher, to 69 percent, among all Americans.

Compared with a month ago, unfavorable views of Cain have soared by 17 points, including by 19 points among Republicans. From essentially an even split in mid-October, more Americans now see Cain unfavorably than favorably by 44 percent to 29 percent. (See separate story.)

One result has not changed: About two-thirds of Republicans and Republican-leaning independents say the issue won’t affect their decision whether to support Cain for the presidential nomination. Still, about a quarter say it makes them less likely to back him.

And the results in any case raise questions about the extent to which Cain can maintain his support, much less expand it, given the controversy’s current trajectory.

GENDER — One key challenge for Cain in this poll, produced for ABC by Langer Research Associates, is a sharp gender gap across results. Leaned Republican women, for example, are nearly twice as likely as men to say the allegations make them less likely to support Cain, 34 percent vs. 19 percent.

Leaned GOP women also show the sharpest increase in views that it’s a serious matter — up by a vast 31 points, from 40 percent Nov. 3 to 71 percent now. Far fewer leaned Republican men, 52 percent, call it a serious matter, and that’s risen by just 14 points.

There are gender gaps in believability as well. Among all adults, men divide evenly on whom they tend to believe. But women, by a wide 50-29 percent, say they’re more apt to believe those who’ve made charges against Cain than to side with his denials.

Leaned Republican women, likewise, are more disposed than are GOP men to believe Cain’s accusers. Forty percent of these women do so, vs. just 22 percent of leaned Republican men.

Among other groups, Cain is maintaining better favorability among “very conservative” leaned Republicans, a core element of his support. Another cause for concern though, is that even in this group, 61 percent now call the issue a serious one, up 28 points in the past tumultuous week and a half of the Cain campaign.

METHODOLOGY — This ABC News/Washington Post survey was conducted by landline and cell phone among a random national sample of 1,018 adults from Nov. 9-13, 2011. The results have a margin of sampling error of plus or minus 3.5 points. This survey was produced for ABC News by Langer Research Associates of New York, N.Y., with sampling, data collection and tabulation by SSRS/Social Science Research Solutions of Media, Pa.