This primary season’s debates have been particularly influential and revealing. The political news audience has become segmented even in conservative circles (for some conservatives, for instance, National Review is the touchstone; for others, it’s the sell-out establishment), but the debates provide a joint viewing opportunity, after which everyone can argue, discuss and interpret the events. In a multi-candidate field with no consensus choice, they also provide critical opportunities to compare and contrast the candidates, many of whom were only barely known before the campaign.

The debates have provided openings, first for Rep. Michele Bachmann (R-Minn.) and then for Herman Cain, to emerge from relative obscurity. But they have also been toxic for Tim Pawlenty and then Texas Gov. Rick Perry. They have provided Mitt Romney with a forum to show his polish and knowledge of the issues.

Tonight Herman Cain may find himself in the hot seat, a bit hotter than even last time. If Rick Santorum, Bachmann, Perry and Newt Gingrich are to have a chance, especially a breakout moment in Iowa, they will have to leapfrog over Cain and gain back a chunk of the social conservative vote. Unfortunately for Cain, he’s left them some openings. His comments on Sunday opposing a constitutional amendment banning gay marriage already set off alarm bells with Christian conservatives. His 9-9-9 plan is being lambasted by fiscal conservatives. Ramesh Ponnuru reminds us that Cain’s plan is actual a three-step reform in which the middle step is the 9-9-9 scheme. (If you doubt we could get through a single re-invention of the the tax code, imagine how ludicrous it would be to attempt it three times.) Ponnuru recaps some of the central flaws in the plan:

At last week’s debate, Cain claimed that poor people would come out ahead under his plan (Stage Two of it, that is) because they would pay a 9 percent income tax, but the standard 15.3 percent payroll levy would be eliminated. On this point he is deeply mistaken. The earned-income tax credit currently offsets some of that 15.3 percent, and he would abolish that credit. Poor people would also pay the 9 percent sales tax every time they buy groceries or get a medical bill.

And that’s not all. Cain is counting the employer share of the payroll tax in his 15.3 percent on the theory that employers pass that on to workers by cutting their wages. He is right to do so. But a good chunk of his VAT would also be passed on to workers. Today’s corporate income tax allows companies to deduct wages. The VAT doesn’t: It is designed to be, at least partly, a tax on wages -- just one that is collected from companies rather than earners. A portion of the VAT would also be passed on to consumers in the form of higher prices.

So in addition to paying new taxes on their purchases and losing the personal exemption and earned-income tax credit, people at the low end of the income scale would see their wages drop. . . .

Even if, per impossibile, Cain were elected president, Congress isn’t going to tell senior citizens that, after having paid taxes on income all their lives, they will now incur extra sales taxes when they spend the money. It’s not going to raise taxes on millions of poor and middle-class people.

And his lack of foreign policy knowledge is an avenue for Bachmann (who is on the House Select Committee on Intelligence) or Santorum to challenge his competency and qualifications. At some point, his share of the electorate will have to come down if these single digit-candidates want to move up. They and he both know it.

Cain and others also have to be aware of the separate audiences they are playing to. The debate has a national audience, but viewers in Iowa, New Hampshire, Nevada and South Carolina are precious to the candidates. If they refuse to denounce Pastor Robert Jeffress, do they lose Mormon votes in Nevada? If Santorum and Bachmann make a point of the others’ absence from Iowa, do they score some points in Des Moines and Ames?

Aside from Cain, there are pitfalls for the other candidates. Perry in the last debate ducked questions about his jobs plan. Since then, he unveiled an energy plan that borrows heavily from other candidates. His competitors will certainly point that out. As I reported Sunday, there is a good deal of accounting gimmickry in his latest state budget and in his current campaign finance reporting. Now, the New York Times reports he underpaid a Texas businessman, who is under investigation by the SEC and state regulators, for use of a private jet, thereby lowering his expenditures. (The Perry camp is pleading confusion about the finance laws.) He will also likely be asked to explain his answer from the last debate that asserted that crony-capitalism deals are fine, so long as they are at the state level.

The greatest peril for the candidates is that the debates confirm the conventional wisdom about their flaws and they fail to break out of their ruts. Perry has not yet shown a command of the issues or explained how his Texas experience really does translate into Oval Office competency. Rather than burnish his executive credentials, his campaign has made him seem inept and his Texas “miracle” less his doing than advertised. Santorum’s conservative intensity has obscured the fact that he’s one of the most experienced conservatives on the stage. Cain hasn’t shown mastery of, let alone proficiency in, a wide range of topics. In other words, it is incumbent on the anti-Romney competitors to shake things up. If they don’t exceed expectations and show the voters something fresh, they’re going to remained mired in single digits well behind the leaders.

If the danger for his opponents is failing to alter the status quo, Romney’s risk in these settings is the unexpected question (last time it was on bank bailouts) or appearing dismissive of the other candidates. So far he has resisted the temptation to take swings at Cain, but at some point he may need to fully engage and do so without sounding condescending or making Cain appear a sympathetic figure. It’s one thing to throw an elbow at Perry ( “I’m talking here” he told Perry in New Hampshire, putting the aggressive governor back on his heels) or to hit the unlikable Jon Huntsman for misrepresenting his record at Bain (as he did last time), but he’d be wise to let Cain’s opponents and Cain himself inflict most of the damage.

There are perils for the moderators as well. They too have settled into a rut. We really don’t need to ask Rep. Ron Paul (R-Tex.) foreign policy questions; we know he’s an extreme isolationist. But we don’t know much about the candidates’ views (other than Romney’s) on China. I don’t think we need to go another round on illegal immigration (which is far down on the list of voters’ concerns nationwide), but few if any questions have been asked about appointment of judges, education policy, defense spending and a host of other issues. Nor have we had a full-blown discussion of the proper relationship between business and government. Is Perry really a free-market guy, or is he a states’ rights crony capitalist? Who’s going to stand up for tax reform that will eliminate special breaks for some industries? In short, there is plenty of unplowed ground, and at this stage in the process the real risk for the questioners is irritating predictability.