The Republican presidential primary race has changed significantly since the last debate, two national polls show on the morning of tonight’s forum on economics in New Hampshire.  Gallup’s survey has the three top GOP contenders within five points of each other, with Herman Cain fighting Mitt Romney for first place:

Republicans’ support for Herman Cain has surged to 18%, their support for Rick Perry has sagged to 15%, and their support for Mitt Romney remains relatively stable at 20%. However, Romney’s support is matched by the 20% of Republicans who are unsure which candidate they will back for the Republican nomination in 2012.

Gallup’s Oct. 3-7 update of Republicans’ preferences for their party’s 2012 presidential nominee shows that Romney since mid-September has regained a numerical lead over the rest of the field, mainly because Perry’s support has dropped by half over the same period. At the same time, support for Cain has more than tripled, from 5% to 18%, creating a competitive three-way race for the nomination between Romney, Cain, and Perry — all within five percentage points of each other. Prior to now, Gallup has had Romney out front, Perry out front, or a two-way battle between them.

Also of note in the new results are Ron Paul’s return to single-digit support levels, and the failure of Michele Bachmann, Newt Gingrich, Rick Santorum, and Jon Huntsman to make significant gains.

The takeaway from that analysis is that the race has come down to these three men, but that may not be entirely true.  Until a spectacular answer on ObamaCare in the previous debate, Cain trailed Paul and tied Gingrich and Bachmann down in the soup.  It’s possible, although perhaps unlikely, that one of the second-tier contenders could hit a home run and draw support from any of the three at the top of the current Gallup poll.

Why unlikely?  Cain already had a high favorability score previous to the debate, and the big issue for him is perceived ability to contend for the nomination and the general election win.  His performance in the last debate and a series of straw-poll wins may be erasing that concern, at least temporarily.  For the other contenders, who are more well-known, replicating the magic that Cain has worked in the last two weeks would be much more difficult.

The bigger surprise at this point is Perry’s standing relative to the other two.  A five-point distance from the lead isn’t exactly Everest at this stage, and he’s within the margin of error with Cain for the Not-Romney position.  If Perry has a good debate tonight and another in Las Vegas next week, his support may rally as a more traditional choice to defeat Romney and then Barack Obama, with the Texas job-creation story as the foundation of the election debate next year.

Quinnipiac’s poll shows it more of a two-man race in Virginia, where Perry once thundered to a substantial lead, but Perry still lurks within striking distance:

Businessman Herman Cain ties former Massachusetts Gov. Mitt Romney as the leading choice of Virginia Republicans for their presidential nomination with 21 percent each, followed by Texas Gov. Rick Perry with 11 percent, less than half his showing a month ago when he had led the pack, according to a Quinnipiac University poll released today.

President Barack Obama’s job approval and re-election numbers remain seriously under water in Virginia, although he is in a statistical tie with Romney and Cain, while holding a narrow lead over Perry, in general election matchups, the independent Quinnipiac (KWIN-uh-pe- ack) University poll finds. …

“Herman Cain is moving up the ladder at breakneck speed. His 21 percent share of the GOP primary vote is more than three times the 6 percent he received when Quinnipiac University surveyed Virginians September 15,” said Peter A. Brown, assistant director of the Quinnipiac University Polling institute. “The race among Virginia Republicans remains far, far from settled. Romney’s support remains relatively stable while other candidates rise and fall around him. Perry led the GOP pack with 25 percent in September followed by Romney with 19 percent.”

That’s more like bad news for Perry, especially in a Southern state which should be more favorable to a Southern governor. Cain has stolen Perry’s thunder in a state that will have a higher profile in the general election than in the primaries, so it’s not the end of the world for Perry, but it’s a good indicator of his slippage. For Cain, the best news from this poll isn’t necessarily the tie with Romney, but the fact that Obama essentially gets the same level of support against Cain (45%) as he does against Romney (44%), although Romney edges Obama while Cain still slightly trails the President. That also erodes the electability concern about Cain and gives him more momentum to claim that a non-traditional candidate has at least the same opportunity to beat Obama as a traditional candidate — especially, perhaps, Mitt Romney.

Cain has a great opportunity to amplify his recent gains with a skillful debate performance tonight, which means that everyone else on stage — except perhaps Romney — has an incentive to attack Cain for the first time in these forums.  Will they, though, especially in a debate that is focused on Cain’s strong suit of economics?  In my column for The Week, I predict that some may choose to hold their fire until next week:

First, the only person on stage with Cain’s business experience is Mitt Romney, and Romney won’t want to go after someone who is polling below him. Romney wants to get back to acting and sounding like a nominee by attacking Barack Obama instead of Perry or anyone else on stage in New Hampshire. With Perry sinking, Romney might not bother responding to Perry’s inevitable attack on RomneyCare at all, reverting back to his strategy of denying his opponents any opening. Romney wants to win these debates by not losing, and so far he has a long winning record at doing just that.

Cain will likely take some heat from other candidates, perhaps on his 9-9-9 tax plan. Conservatives like Cain, but they have fought the idea of an additional consumption tax for years. Michele Bachmann would have an opening to attack Cain on adding a new 9 percent sales tax, while Rick Santorum can challenge the impact that the new consumption tax will have on lower-income families. Newt Gingrich has been chummy with Cain on stage and loath to attack anyone, but Gingrich needs a game changer if he wants to ever have a shot in this campaign, and he can address the potential pitfalls of policy better than anyone else in the debate.

Still, don’t expect too much criticism of Cain in this debate. Unlike Perry or even Romney, Cain doesn’t have a record of governance — and therefore doesn’t have to account for any of the necessary compromises that come with the job. That in itself could form the basis of attacks if not for the anti-establishment mood that fuels Republican primary voters in this cycle. Even Romney has flogged himself as someone who isn’t a lifelong politician despite running for significant office in 1994, 2002, and 2008. Going after Cain on a lack of public-sector experience practically makes Cain’s pitch for him.

Of course, Romney might surprise us tonight, and he previewed a potential line of attack yesterday:

Romney drew a contrast between his resume, which includes four years as governor of Massachusetts, and Cain’s, which does not include elected office. After talking about his experience going from Bain Capital to the governor’s mansion, Romney suggested that Cain was, perhaps, not quite as ready as he is for the Oval Office.

“I was able to find ways to use my skills in a public sector setting, probably something — if I were Herman — I’d say I wish I had that too because you don’t want to necessarily learn that for the first time as the president of the United States,” Romney said.

Romney’s jab at the former Godfather’s Pizza CEO came in response to a question from a college student who has asked Romney to contrast himself with Cain. It came on a day when a new poll of New Hampshire voters conducted by Harvard University and St. Anselm College showed Cain running in second place behind Romney, 38 percent to 20 percent.

It’s going to be hard to argue that voters should back Romney because he’s not a career politician — a theme he has sounded now for weeks after Perry’s entrance in the race — and then attack Cain for, er, not being a career politician.  We’ll see if Romney can pull off that trick tonight, or whether he wants to try it at all.