The Wisconsin Voter The Journal Sentinel's Craig Gilbert explores political trends in a purple state and beyond. SHARE Click to enlarge

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Roughly $16 million has been spent in the Wisconsin governor’s race on broadcast TV ads, most of them attacking the other side’s candidate.

But if those ads are changing minds, it’s awfully hard to tell.

Wisconsin voters have remained almost perfectly divided over Gov. Scott Walker and Mary Burke for months, no matter what has happened in the race, no matter what has happened in the state, no matter what has happened in the world, no matter what the campaigns have said or done.

Back in March, about half the state’s voters viewed Walker positively and about half viewed him negatively.

Seven months and thousands of ads later, that hasn’t changed.

Back in March, most people didn’t know who Mary Burke was. But of those who did, about half viewed her positively and half viewed her negatively.

Seven months and thousands of ads later, that hasn’t changed. As her name recognition has grown, her positive and negative ratings have risen in almost perfect lockstep. Burke was a 50-50 candidate when nobody knew her. And she is a 50-50 candidate today.

Why has there been so little measurable change in this contest from week to week and month to month?

Why have both candidates more or less withstood the efforts of their opponents to drive their “negatives” through the roof?

The obvious answer is this state’s deep and unyielding divide over its governor, which has all but ensured a close and competitive contest with only tiny swings in public opinion.

Another answer may lie in a financially competitive campaign where neither side has outshouted the other or gained the upper hand in the message wars.

Burke and her allies have spent $8.2 million on broadcast TV, Walker and his allies $7.4 million, according to the Center for Public Integrity. That has produced a far more level playing field than the 2012 recall fight when Walker dramatically outspent his opposition.

“It’s evidence the campaigns have been pretty balanced, with neither one putting through an argument that has really penetrated outside their base and beyond a majority,” says Charles Franklin, who conducts the Marquette University Law School Poll.

Of those $16 million in ads, about three-quarters have contained attacks on the other side’s candidate.

Yet Walker’s “negatives” — the share of voters who view him unfavorably — have scarcely budged all year. That number has been firmly stuck at 47% or 48% in six of the seven polls Marquette has taken since March.

The consistency of Walker’s polling numbers should come as no surprise, given how entrenched public opinion about him has been through most of his first term. Attitudes toward the incumbent in this race are almost cast in concrete.

More striking is how consistent Burke’s numbers have been.

She entered this race a political blank slate, vulnerable to attack because people knew so little about her. Yet her public standing has neither improved nor declined as she has become better known. Her positives and negatives have climbed in tandem. Voters have remained almost perfectly divided in their perceptions of her no matter how much they know about her. In Marquette’s last poll taken Oct. 9-12, her ratings were 40% favorable and 43% unfavorable among registered voters, 44% favorable and 44% unfavorable among likely voters.

Burke’s lack of a political record has made her a tougher target to attack than Walker’s 2012 and 2010 opponent, Milwaukee Mayor Tom Barrett.

And the 50-50 divide over Walker has helped ensure that voters would be split right down the middle over her, as well. In a recent poll by St. Norbert College and Wisconsin Public Radio, 61% of Burke voters said the primary reason they support her is they don’t like Walker and his policies.

Marquette’s polling suggests that Burke has weathered the ad wars in better shape than Barrett and in better shape than the candidates in the 2012 U.S. Senate race, Tammy Baldwin and Tommy Thompson.

That Senate race was a great example of the power of campaign advertising. It was one of the most negative races the country, and those attacks took a toll on both candidates.

By the closing weeks of the campaign, Baldwin’s negatives (the share of voters who viewed her unfavorably) had outstripped her positives (the share that viewed her favorably) by 16 points in one Marquette poll and 8 points in another.

Thompson fared even worse. Battered in an unanswered late-summer wave of attack ads, he finished the race with a majority of voters — 51% — viewing him unfavorably, and only 37% viewing him favorably.

By contrast, the Walker-Burke race is a great example of the limits of campaign ads.

It doesn’t mean all those television spots are having no effect. It doesn’t mean the ad wars are irrelevant.

It just means that whatever impact the ads are having on public opinion is marginal and hard to detect. It’s very hard for campaigns to change minds when attitudes about the incumbent are as partisan, polarized and unyielding as they are in Wisconsin.

Follow Craig Gilbert on Twitter @WisVoter