"Campaigns matter." That's a Star Tribune Editorial Board maxim that bears invoking as the 2010 general-election campaign commences one month earlier than it traditionally has in Minnesota.

The field of candidates for governor is set. Voters in the three major-party primaries last Tuesday sent a lawyer-legislator, a former U.S. senator and a public-relations professional to vie for the chance to tackle the most difficult problems to confront state and local governments in more than a generation.

The importance of this gubernatorial election makes the primary date change fortuitous. It provides extra time for voters to examine the major-party nominees, their campaigns and their proposals. We're watching to see whether and how the candidates meet three distinct challenges.

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TOM EMMER has been bold in offering to set state and local government on a course quite different from the one it has been on for half a century. But the Republican nominee also has been unspecific and at times evasive. He said in a Minnesota Public Radio interview in April that total state spending "could easily" be cut 20 percent, then balked later when reporters said he had suggested a 20 percent cut. His website touts the virtues of lower taxes but does not definitively call for them. Neither does it say how he would manage further revenue reductions when the state already projects a $6 billion gap between revenues and scheduled expenditures in 2012-13.

Emmer's challenge is to assure voters that if he's elected, the services Minnesotans need and expect from state and local government would continue at a level a prosperous and compassionate society requires.

He cannot expect Minnesotans to believe that after eight years of Republican Gov. Tim Pawlenty's "no new taxes" rule, $6 billion in unnecessary spending remains in a $38 billion budget. School districts in this state are already switching to four-day weeks and are overcrowding classrooms. Nursing homes dependent on state reimbursement are closing in rural areas. Routine medical care is being denied the poorest Minnesota adults.

Emmer should explain how he plans to remedy those problems. Until he does, he can expect to stand accused of proposing to make them worse. He has said he might not reveal a full budget proposal until October. That's too late.

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MARK DAYTON'S challenge is quite different. The DFL nominee has been forthright in saying that he plans to rely on an increase in state income taxes for the top 10 percent of earners to close nearly two-thirds of the state budget gap.

That proposal propelled him past two formidable challengers in the DFL primary. But it has also alarmed a significant share of the state's business community and more moderate Minnesotans.

Dayton is asking for Minnesota to again make its top personal income tax rate one of the highest in the country. That's where it ranked 25 years ago -- when a DFL governor, Rudy Perpich, pushed hard for its reduction to improve business competitiveness.

Since then, competition among the world's economic centers for capital and talent has dramatically intensified. Dayton's challenge is to demonstrate greater sensitivity to the competition Minnesota faces. He would do well to listen to the state's business leaders and respond to their concerns. He'll have a good chance to do as much Tuesday at the Minnesota Chamber of Commerce debate in Nisswa.

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TOM HORNER'S challenge is akin to the one that faced the last two Independence Party candidates for governor, Tim Penny and Peter Hutchinson. Like them, Horner is a centrist steeped in public policy. Like them, he's handicapped by an underfunded campaign and an undersized political party.

His challenge is to build a campaign that's large, visible and appealing enough to dispel doubts that he can be elected -- or that, if elected, he could be effective as a third-party governor. He needs a clear and compelling message, delivered early and often via the public airwaves. And he needs convincing answers to questions about how he could overcome the animosity of both parties at the Legislature that awaits any third-party governor.

Horner's challenges are not his alone to meet. They are shared by Minnesotans who favor multiparty politics and want it to flourish in this state. Those who want Horner to be more than a spoiler in this election should be on notice that for that to happen, he needs more than their votes on Nov. 2. He needs their money and their time now.