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Wisconsin is back to a very familiar place in the partisan political wars, according to the latest poll by Marquette Law School: almost perfect parity.

President Obama leads Mitt Romney 49% to 48% in a survey of 870 likely voters taken Oct. 11-14.

Two weeks earlier, Obama led by 11 points in Marquette’s polling.

The story in this state is the same as elsewhere: Romney’s gains since the first presidential debate Oct. 3 have erased Obama’s post-convention bounce and made the race as close and unpredictable as it has been at any point in this election year.

The battle for Wisconsin has now gone through four distinct phases since mid-summer. From July to early August, Obama led by mid-single digits (averaging state surveys by different pollsters). Then Romney picked Wisconsin’s Paul Ryan as his running mate on Aug. 11 and most of Obama’s lead disappeared. Then the conventions boosted Obama, wiping out the “Ryan bounce,” giving the Democratic ticket an average lead of almost eight points in seven separate September polls. And now the Oct. 3 debate has wiped out Obama’s convention bounce. Marquette found that Romney had a two-point lead among those who watched that debate; Obama had an eight-point lead among those who didn’t.

In four Wisconsin surveys since Oct. 3 (by Rasmussen, Quinnipiac, Public Policy Polling and Marquette), Obama’s leads are two, three, two and one point. The fact that the US Senate race is also a virtual tie in Marquette’s poll (46% Thompson, 45% Baldwin) underscores the state’s current competitiveness, far more reminiscent of 2000 and 2004 than 2008.

The shifts in Wisconsin these past three months haven’t been massive. (The swings have been bigger in Marquette’s polling, smaller in other state surveys). But in an election where the share of undecided voters is unusually small, they’re a sign of play in the electorate. The battle for Wisconsin has basically oscillated since mid-summer between a quasi-comfortable Obama lead and a tiny, tenuous Obama lead (the chart below reflects polling by Marquette, NBC, Quinnipiac, CNN, Rasmussen and Public Policy Pollng):

There are at least two ways to read this pattern. One is that even at his upper range, Romney is only at or just below parity. If Romney’s two mini-surges (post-Ryan, post-first debate) represent his ceiling, then he may be destined to lose Wisconsin. He has led in only three of nearly 40 independent Wisconsin polls this year. Based on history, it would be very unusual to carry a state with that election-year track record.

The other way to read the pattern is more favorable to Romney: Wisconsin has tightened for the second time in two months and it’s extremely competitive again. If Romney’s recent gains represent a trend-in-progress – if he’s got more room to grow – then Wisconsin is perfectly winnable.

More important, some underlying voter attitudes have gotten better for him since his debate performance in Denver. Romney has been hobbled all year in Wisconsin by poor favorability ratings. In Marquette’s surveys, perceptions of him have consistently been more negative than positive. In six Marquette polls from June through September, the share of likely voters who viewed him favorably never deviated from 38 or 39 percent; the share that viewed him negatively ranged from 44 to 54 percent.

But in Marquette’s latest poll, Romney got his best numbers of the year: 46% favorable and 48% unfavorable. That’s worse than Obama’s ratings, which have been very consistent, ranging from 53 to 55 percent favorable and 41 to 45 percent unfavorable. But it's a significant improvement for Romney:

Romney’s image improved in other ways in Marquette’s survey: more people than before now see him as a strong leader (up from 47% to 55% since the Oct. 3 debate) and more people than before say he “cares about me” (up from 39% to 47%).

All the same questions apply to the national picture. Are Romney’s gains just bringing the race back to where it was before the two conventions (close but meaningful Obama advantage in the battlegrounds)? Have they already turned it into a pure toss-up? Or do they augur a fundamental breakthrough for Romney that could give him the upper hand in this election?

Did the second presidential debate Tuesday, in which Obama was far more forceful than he was in the first debate, shift any ground? (It’s too soon to measure its impact in the polls). Will the third and final debate next Monday on foreign policy be a factor?

Averaging the national polls right now gives you a tie (47% Obama, 47% Romney in the RealClearPolitics polling average), even though individual polls point in different directions: Romney is up six in Gallup’s tracking but down three in the recent Washington Post/ABC poll.

Averaging the state polls has until now pointed to an Obama electoral edge, but the margins are very small and the numbers are fluid.

History, too, sends mixed signals.

Election scholars design forecasting models for presidential races, based on the correlation between the popular vote and a handful of key factors such as incumbency, economic trends and pre-election presidential approval ratings. These are predictions based largely on fundamental conditions, as opposed to shifting campaign dynamics.

Of 13 election forecasts recently published in PS, the journal of the American Political Science Association, five predicted Obama would win the popular vote, five predicted Romney would win, and three pointed to a toss-up.

The average of all 13 forecasts was a microscopic Obama popular vote margin of three-tenths of one percentage point.

UPDATE: A new NBC/Wall Street Journal/Marist poll was released Thursday night showing Obama leading Romney 51% to 45% in Wisconsin, almost identical to NBC's September poll. The biggest difference between the NBC poll and a few other recent Wisconsin polls, especially Marquette's, is that NBC shows no gains by Romney here since last month. Marquette showed a ten-point swing in Romney's favor from its September poll; Quinnipiac showed a three-point swing from its September poll; PPP showed a five-point swing from its September poll; and Rasmussen showed a one point swing. But aside from that, the polls are pretty consistent about the current state of play in Wisconsin: Across these five different Wisconsin surveys, Obama's support ranges from 49 to 51 percent; and Romney's ranges from 45 to 49 percent.

Follow Craig Gilbert on Twitter @WisVoter