Michigan voters may already feel as if they’re inundated with political advertising preoccupied with nasty personal attacks.

But Labor Day marks the traditional start of the campaign season, and they ain’t seen nothing yet.

With competitive races for governor and the U.S. Senate, as well as four open congressional spots and every Legislative seat up for grabs, the sprint to Nov. 4 may well be the most expensive campaign stretch in Michigan history.

Projections are that the Senate match-up between former Secretary of State Terri Lynn Land on the Republican side and Democratic Congressman Gary Peters will cost $50 million or more.

Unfortunately, much of the advertising so far has been aimed at demonizing the candidates.

Both Land and Peters have solid records of public service, and have proved themselves committed to the interests of Michigan voters.

Neither deserves the tarring they are receiving.

And Michigan voters certainly deserve more clarity on what each will add to the Senate if elected.

We hope at least some of the future campaign ads are centered on ideas for addressing the considerable problems faced by the nation and world at this critical moment.

The governor’s race is also polling close. Republican Gov. Rick Snyder begins the post-Labor Day campaign locked in a virtual dead heat with his Democratic challenger, Mark Schauer, according to polls.

That race will also draw huge stacks of outside money if the next round of polling results remains close.

The worry here is that so much of that spending is being aimed at denigrating Michigan’s comeback.

Snyder has been touting the state’s progress over the past four years.

Schauer’s backers seem convinced they must counter his message by crafting an image of Michigan as a still failing state.

That’s politics, and as we said, this is the peak of the political season.

But the potential damage of those doom and gloom ads goes beyond the impact on Synder’s reelection hopes; they actually risk hurting Michigan’s fragile recovery.

The state has worked very hard to erase the negative impressions of Michigan’s economy held by job creators and investors.

Michigan has moved steadily up in the rankings of states with the most favorable business climate, and its performance numbers back the better image.

Measures from Gross Domestic Product to household income and the creation of good-paying jobs (all now above pre-recession levels) send a positive message about Michigan’s direction.

Schauer may be able to make a credible case that the improvement has been too slow and his leadership would accelerate it.

If so, he should share his ideas and proposals with voters.

A lot of campaign money will be spent in Michigan over the next nine weeks.

We expect there to be politics, and welcome it. But all candidates should be careful about destroying hard-built reputations, and to not rain on Michigan’s parade.