Herman Cain is under fire for alleged sexual harassment, which his campaign is now flatly denying. What can we say about all of this? Two quick points:

1. Amateur presidential candidates are more likely than career politicians to be tripped up by past indiscretions. This is because they’ve never been vetted politically before. For career politicians, chances are that many of the embarrassing indiscretions of the past have been dug up and aired publicly by opponents in previous campaigns. This is only natural; opposition researchers exist at all levels of politics, and very few campaigns have any misgivings about using what they find if they think it at all effective. And thus when faced with two  presidential candidates, one amateur and one career politician, you are looking at two very different people in relation to scandal. All else equal, the career politician is

(a) less likely to have something in the past that could ruin a career, as there’s a real chance it would already have been found by a previous opponent; and

(b) more likely to have already dealt with and controlled small to medium-sized issues from the past, neutralizing their effectiveness if recycled.

And thus any career politician who becomes a presidential candidate has survived an evolutionary test for scandal; natural selection has not exposed a disqualifying scandal, and has partial-immunized him from many minor allegations that have already surfaced. The unvetted amateur, on the other hand, stands at the first stage of the evolutionary process. Think you’re going to find a silver bullet scandal in president Obama’s past at this point? Not a chance. Think Romney’s groundskeepers-who-employed-illegals is going to make above-the-fold news years after it first came out? Doubtful. Think a random chattering-class amateur-cum-politico has a past indiscretion or two?  You bet.

Now, presidential campaigns expose all candidates to a level of scrutiny and opposition research that is unparalleled, regardless of previous political experience. But that’s kind of the point: it’s all coming out when you submit yourself to the presidential election machinery. For career politicians, that means the last scrapings from the bottom of a well-traveled barrel. For amateurs, it means the same scrapings, plus all the low-hanging fruit. Both can be good sources of fodder. But they are far from the same thing.

2. I’m surprised some people think this won’t hurt Cain. Last night on Twitter, both Ryan Lizza and Rich Lowry indicated that Cain might not be damaged by this story. The theory goes something like this: Cain will effectively spin the story as an example of the high tech lynching he already predicted from the liberal media, and conservatives, in turn, will rush to his defense, making him more popular than ever. And this morning, we do indeed find some conservatives coming to his defense.

It sounds plausible, but there are at least four problems with the theory: first, Cain isn’t competing against the liberals right now. He’s in a primary against other conservatives. Unless the allegations are completely baseless and can be proven as such, it’s going to be tough to sell this as the liberals smearing him. It may be done quietly, but if this story has legs, it will be kept alive by his primary opponents, not the Democrats. More to the point: is it really the case that the Democrats would rather face Romney? That doesn’t pass the smell test.

Second, GOP primary voters aren’t being forced to choose between a flawed Cain and a Democratic candidate;  the political cost of abandoning him is very small, and thus the incentives to rally behind him are very low. It’s one thing to hold your nose and vote for someone with a flawed-character if the cost of abandoning him is a partisan loss in the election. But, if anything, the opposite is true here. And all  just for a chance to stick it to the liberal media? Cain may get a sympathy bump from the right, but it won’t last if the story pans out. For the same reasons, I don’t buy the analogy to Clarence Thomas.

Third, one of Cain’s big selling points right now is his very low negatives among voters. This is bound to affect that, even if it didn’t injure his overall support. Part of his popular appeal, I think, is the public sense that he’s not an ordinary politician. A scandal like this will start to break down that narrative. Even if the allegations don’t reshape how people view him, the campaign’s response to them probably will.

Fourth, I don’t see how this helps Cain’s fundamentals. He still has no endorsements from federal elected officials and very little in the way of fundraising. This will probably solidify those realities. I don’t think party actors were giving him much of a look before, but now they won’t touch him, even if only because they get nervous about what else is hiding in the closet. It’s just more potential risk in a year that the party wants to reduce variance. If Cain can survive a medium-sized scandal and win this nomination, it will definitely be reason to re-assess our understanding of party influence on the presidential nomination process.

Now, I was already on the record believing that Cain had almost no chance at the nomination. In that sense, I guess this strikes me more as a time/place/manner thing that something that actually affected the future. Perhaps the biggest effect, one way or another, will be on book sales and speaking fees. In fact, my first reaction to the breaking of the scandal was that it probably let the observers/pundits who were bullish on Cain off the hook with an excuse for what I see as an inevitable crash.

But part of me thinks that things like this should be built into any estimation model. Everyone has past indiscretions, at least minor ones. Was it really going to be possible for Cain to get through the nomination process without them being dug up? I’m not saying that I thought about this much before yesterday, or that scandal was the likeliest way for Cain to be brought down. But given his unvetted status, it was always a possibility.

As of 7am this morning, Cain is down 36% on Intrade. There’s certainly a chance he could recover from this and reverse those numbers. But this was always a campaign teetering on the brink. My guess is this is the beginning of the end.