Herman Cain has hit yet another roadblock in his presidential campaign, and this one may be the biggest of all.

We don’t know whether allegations of inappropriate behavior with two women during his time as head of the National Restaurant Association in the 1990s will bring the new GOP frontrunner down. But given the seriousness of the allegations — and the lack of a firm denial from Cain’s campaign that the women were given out-of-court settlements — it’s worth a look at who would benefit from the Cain wave rolling back.

Luckily, an NBC News/Wall Street Journal poll earlier this month asked people not only their first choice for president, but their second as well. And that allows us to get a picture of the race with a diminished Cain.

Republican presidential contender Herman Cain addresses an audience at the American Enterprise Institute for Public Policy Research Monday morning. (KAREN BLEIER/AFP/Getty Images)

* Mitt Romney: The former Massachusetts governor appears to have more to gain than anybody else, as his share of the vote in a race without Cain rises from 23 percent to 32 percent. This is notable because Romney has yet to crack 30 percent in any major poll of the crowded GOP primary field. The poll suggests that, with the latest Romney alternative flaming out, the longtime frontrunner would start to pick up some of the supporters who may have been searching for an alternative for the last several months. This, of course, has been the Romney campaign’s hope for a long time.

* Rick Perry: It stands to reason that the Texas governor could recover some of the ground he lost to Cain, and the polling bears that out. Without Cain in the race, Perry climbs from 16 percent to 22 percent — the second biggest rise behind Romney. It should be noted, though, that the NBC/WSJ poll was conducted before the extent of Perry’s free fall had been realized, and other recent polling shows him well below that 16 percent figure. At the same time, it wouldn’t be surprising to see Perry benefit from Cain’s loss, given how much money he has and his just-launched ad campaign.

* Newt Gingrich: Perry might have to split any gains with Gingrich, mostly because the former House speaker is on a better trajectory. Solid recent debate performances have elevated Gingrich back into the ranks of potential contenders, and if voters start seeing him as a legitimate candidate again, Cain’s supporters might jump on board. The NBC/WSJ poll shows Gingrich rising from 8 percent to 12 percent without Cain in the race, but we suspect Gingrich has improved his stock even more than that since the poll was conducted, while Perry’s stock has fallen further. (It should also be noted that Cain and Gingrich have been more friendly with each other than perhaps any two candidates — they appeared on CBS’s “Face the Nation” together and will be holding a Lincoln-Douglas-style debate with each other next month — and maybe Cain’s supporters would appreciate that when they are looking for alternatives.)

* Michele Bachmann: The poll shows the Minnesota congresswoman also gains 4 percentage points, rising from 5 percent to 9 percent. Few see Bachmann asserting herself as a frontrunner again, but if there is an anti-Romney void in Iowa, Bachmann may be the most likely candidate to fill it. The most recent Des Moines Register poll, released over the weekend, shows Bachmann in fourth place at 8 percent, but with Rep. Ron Paul (R-Texas) stuck in the low teens, Bachmann would be the next candidate behind Romney to gain, and polling has suggested that Romney doesn’t have too much room to grow in Iowa.

Q&A Transcript

" In the wake of harassment allegations, is Herman Cain done as a serious GOP contender?"

Aaron Blake

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