Gov. Mark Dayton holds a double-digit lead over GOP challenger Jeff Johnson with less than two months to the election, but one in five voters have yet to make up their minds about the contest, according to a new Star Tribune Minnesota Poll.

Dayton leads Johnson 45 percent to 33 percent, with 20 percent undecided. The poll found that Johnson, a Hennepin County commissioner from Plymouth and former state legislator, is still a mystery to many: At least a third of likely voters did not recognize his name, while another 40 percent had no opinion of him.

A longtime political figure, Dayton has 100 percent name recognition. But Minnesotans are deeply divided on his performance as governor. About 46 percent approve of the way Dayton has done his job, but 45 percent disapprove. That's a tumble from February's Minnesota Poll, when Dayton registered a 58 percent approval rating.

Despite that notable drop, Dayton's campaign manager said the governor was pleased by the size of his lead over Johnson. "We are grateful that so many Minnesotans recognize the progress our state has made during the past four years," said campaign manager Katharine Tinucci. "The poll tells us to keep working even harder to talk with voters about what we stand for — more jobs for our citizens, the best education for our kids, and government that works better for everyone."

Johnson has argued that lower government spending and less regulation would help the state's businesses grow even stronger, but he has been hampered by a light schedule of public events and little advertising. The poll shows he has work to do in making himself better known to voters.

"We knew going in that one of my jobs would be to raise my name recognition," Johnson said. Despite trailing by double-digits, he said the large number of undecided voters gives him a plausible path to winning in November.

"The key for me is to continue to campaign and to get ads up on television, which we will soon," Johnson said. "Once I start sharing my vision, I would hope it starts to heavily break my way."

Neither campaign has launched its own TV ads yet. But the Alliance for a Better Minnesota, which supports Dayton, has aired several commercials critical of Johnson, and the DFL is launching a $1 million TV ad campaign in support of the governor this week. The Dayton campaign itself has reserved airtime for late September, and Johnson vowed his campaign would be on the air by the end of the month, too.

The poll of 800 likely voters was taken Sept. 8-10 on both land line and cellphones. Its margin of sampling error is plus or minus 3.5 percentage points. In the sample of likely voters, 39 percent identified themselves as Democrats, 32 percent as Republicans and 29 percent as independent.

Hannah Nicollet, the Independence Party candidate for governor, had support from only 1 percent of poll respondents.

In asking for a second term, Dayton is banking that voters will see a link between his leadership and positive trends in the state economy. He also has to hope voters don't lump him in with his fellow Democrat, President Obama, whose 40 percent approval rating is outweighed by 52 percent who disapprove.

Dayton was narrowly elected four years ago, defying a national Republican wave, and has had a busy four years.

In addition to pushing an income tax increase on the wealthy that helped fund a hike in spending on schools and public colleges, Dayton was the chief booster of public funding for the $1 billion Vikings stadium now under construction. He signed bills legalizing gay marriage and medical marijuana, and boosting the state's minimum wage. And he presided over the rocky implementation of MNsure, Minnesota's delivery vehicle for federal health care changes.

"I wasn't sure I'd be happy with Dayton as governor, but I have to say I am," said Bob Rudy, 68, a retired Hennepin County prosecutor and Elk River resident who participated in the poll. "He's done a good job and he's not afraid to take on difficult things."

Rudy still calls himself a Republican but said he's been voting more for Democrats in recent years. "I'm not a real fan of the Tea Party," Rudy said. He's voting for Dayton despite a personal bad experience with MNsure: He helped his daughter sign up for insurance coverage through the site and called the experience "quite frankly terrible."

Even for many voters unwilling to support Dayton, Johnson remains an unknown quantity.

"I don't know enough about Jeff Johnson yet to make any decisions one way or the other," said poll respondent Carolyn Alm, 72, a retired Minneapolis schools employee who lives in Chisago City. Alm, who voted for former state representative Marty Seifert in the GOP primary, called Dayton "a really decent human being" but said she couldn't support him.

"I see a lot of take from the rich and give to the people who do nothing," said Alm, adding that she intends to spend more time reading up on Johnson's views and background.

Johnson is a six-year veteran of the Hennepin County Board and previously served in the state House from 2001 to 2007. He ran statewide once before, losing the 2006 attorney general's race to Democrat Lori Swanson by more than 266,000 votes.

Northern Minnesota changes

Dayton's strongest support in the poll is in Hennepin and Ramsey counties, home to Minneapolis and St. Paul. He trails Johnson slightly in nine other Twin Cities suburban or exurban counties but holds a small edge over him in 43 counties in southern Minnesota. In 33 northern Minnesota counties, Johnson is leading Dayton 42 percent to 34 percent.

While northeastern Minnesota was long a DFL stronghold, it has become more of a battleground in recent years. Dayton easily won northeastern Minnesota's Eighth Congressional District in 2010, but Republicans also won the district's congressional seat that year. And other parts of northern Minnesota have grown more reliably Republican.

Henry Soenneker, a 72-year-old crop farmer from Bluffton in Otter Tail County, said he supported Dayton's income tax hike and would even accept a higher state gas tax to pay for road and bridge improvements. But he said cultural issues make it impossible for him to support Democrats.

"Jeff Johnson is pro-life. Mark Dayton is not. The abortion issue is a decisionmaker for me on a lot of things," Soenneker said. He said the only Democrat he supported in recent years is U.S. Rep. Collin Peterson, but he even stopped voting for him in the last few elections.

Dayton leads Johnson among voters of all ages. He also is ahead definitively among people who earn less than $50,000 a year, at 54 percent compared to 31 percent for Johnson. That divide starts to drop as income rises. However, Dayton's loss tends not to be Johnson's gain. Among those who earn more than $50,000, Dayton gets 44 percent, Johnson comes in at 35 percent, and the number of undecideds rises.

Gender gap

One of the starkest divides in governor's race polling is along gender lines. Men favor Johnson over Dayton 43 percent to 34 percent, but women back Dayton even more strongly: 54 percent favor the governor, compared with 25 percent for the Republican.

"I just believe in our governor," said Deb Myrhe, a 43-year-old public school speech pathologist who lives in Columbia Heights. Myrhe described herself as a "lifelong Democrat" and party-line voter.

Myrhe said a few of Dayton's high-profile moves didn't sit well with her. "I got frustrated with that stadium," she said. But she accepted Dayton's argument that the project has created jobs and will attract new businesses.

Asked if she's formed any impressions of Johnson, Myrhe said she hadn't. "I think I know what he looks like," she said.

Patrick Condon • 651-925-5049

Staff writer Rachel E. Stassen-Berger contributed to this report.