Three years later, Mr. Dayton is trying to revive his political career — this time as a candidate for governor pushing unabashedly for a tax increase and disclosing bouts with depression and alcoholism.
He hopes to claw his way through a field of 11 Democrats to face challengers from the Republican and Independence parties in November. Gov. Tim Pawlenty, a Republican, passed on a third-term bid as he weighs a possible run for president.
Mr. Dayton steps up his campaigning in January — just as he turns 63 — by visiting all 87 Minnesota counties in 87 days. Early on, he'll hit the bone-chilling northern counties bordering Canada.
"If you go in the summertime, they know you're interested," Mr. Dayton said. "If you go in the wintertime, they know you're serious."
Seriousness is what Mr. Dayton is about. He often comes off as stiff in front of a crowd, and has never been known for smooth oratory or political flash. Mr. Dayton wants voters to see him as an earnest leader capable of tackling Minnesota's monumental budget problems in a shaky economy.
But he brings a lot of baggage to the race.
With his Senate term set to expire after 2006, Mr. Dayton opted against running for re-election amid faltering poll numbers and fundraising difficulties. The department store heir had sunk $12 million into his 2000 campaign, and had no plans to dig that deep again.
He left with a jaded view of the Senate and his place in it. He called Washington a "cesspool" and told a group of students that Congress, including himself, deserved "an F for results." Outsiders graded him just as harshly: Time magazine labeled him "The Blunderer" on a list of ineffective senators, citing his widely criticized decision in 2004 to temporarily close his Senate office over fears that terrorism endangered his staff and visitors.
The lowlights have overshadowed what Mr. Dayton regards as the successes of his tenure, from securing money for a pioneering mental health program for soldiers returning from combat to setting up a hot line for people denied claims by their insurance companies.
"I stand on what I was able to accomplish and acknowledge I couldn't accomplish as much I wanted to because of the limitations of being low in seniority and being in the minority," he said in an interview. "For those very reasons, I wanted to seek a position where I could be effective."
Mr. Dayton has served in executive roles before, leading two Cabinet-level state agencies under the last Democratic governor and serving a four-year term as state auditor. Along the way, he had failed runs for U.S. Senate in 1982 and governor in 1998.
The Dayton name is widely known in Minnesota, where the former senator's great-grandfather George Dayton opened a dry goods store that ultimately grew into Target Corp.
Mark Dayton's name recognition and personal wealth make him a legitimate contender for the Democratic nomination. Mr. Dayton has said he will contribute to his own campaign, though he hasn't said how much. He plans to run in the summer primary even if party activists endorse another candidate at their April convention; most in the race say they'll drop out without that earlier seal of approval.
While Republican leaders have rapped Mr. Dayton's political past and his proposal to raise taxes on the richest 10 percent of people in the state, some in the party regard him as formidable.
"There's something appealing about somebody who doesn't need the job. Implicit in somebody not needing a job is that person will try to do the right thing," Republican analyst Sarah Janecek said. "It makes him stand out. Here's a guy who walked away from the most exclusive club in the country."
Yet Mr. Dayton could have trouble turning the debate from his senatorial struggles, said Joseph Kunkel, a political science professor at Minnesota State University in Mankato.
"He's singularly lacking in charisma. By his own admission, his term in the Senate was not too successful. He's not a new face on the scene. He's been around a long time," Mr. Kunkel said. "Those things are going to be real obstacles."
Mr. Dayton threw in another wrinkle in December by revealing that he had long suffered from mild depression and taken medication for it. A recovering alcoholic, he also disclosed that he slipped late in his Senate term and sought treatment in 2007. He said he has been sober since and insisted neither issue would hinder his competence to lead the state.
"I wouldn't be running for governor if I weren't very confident in my abilities and my ability to withstand the pressures of the job," he said.
Mr. Dayton refused to offer specific details about his relapse or medication. "There's a point where I say further details are and properly remain private," he said.
Political allies and foes commended Mr. Dayton on his admission and said it shouldn't be an issue in the race.
To union leader Eliot Seide, it demonstrated the candor that helped earn Mr. Dayton the endorsement of the politically potent American Federation of State, County and Municipal Employees Council 5.
"Mark Dayton is not a politician's politician," said Mr. Seide, AFSCME's executive director. "Mark Dayton doesn't make decisions based on the politics of the moment or his own political needs. We're dealing with somebody who has an immense sense of personal integrity and some font of personal strength."
© Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.