At-large Metro Councilman John Cooper won't run for Nashville mayor this year, and likely won't seek re-election for council either, in an exit from Metro government that he says will let him become a bigger voice on the municipal finance issues that he cares about.

Cooper, long speculated as a challenger to Mayor David Briley, discussed his decision — and the agony it presented — in a interview with The Tennessean.

He said he's "humbled" by the people who encouraged him to run and "tortured" by the feeling of letting anybody down. Calling it a "personal choice," he said he felt he could best serve Nashville by working outside government to "translate" the financial issues plaguing the city for the public.

"After careful consideration over many months, I've decided that I'm not running for mayor, and I want to spend the next phase of my career on other projects and commitments," Cooper said.

"I hope to remain deeply involved in the important conversation that Nashville needs to have about what kind of city we want to be, who is included, who is paying for what, what are we not paying for," he added. "And I need the time, frankly on the personal side, for some other projects and commitments. Government can take 150 percent of your time."

Cooper's decision alters race

Cooper, a first-term councilman who holds the council's top at-large seat, has emerged as the leading critic of the fiscal and budgetary decisions under the last two mayoral administrations, including Briley.

In a Metro era defined by expensive city-financed projects, he's opposed the financing of Nashville's soccer stadium, railed on incentives to private developers as unneeded giveaways and fought a host of deals that involved the city selling public land.

The younger brother of U.S. Rep. Jim Cooper, D-Nashville, the 62-year-old would have been considered a formidable candidate had he entered the race, one who could effectively frame a sharp contrast against Briley.

Metro's mayoral election is Aug.1, and early voting begins July 12.

Cooper, who works as a developer in Williamson County, said he believes he would have been successful had he run. He had already started to assemble a campaign team.

"Would it have been an uphill climb? Sure, it always is against any incumbent," Cooper said.

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But rather than change in the mayor's office, Cooper said, "What's most needed is to educate in a non-political, nonpartisan context."

He said not running will allow him to more effectively inform residents on the fiscal trajectory of the city.

"And I will try to be doing that," Cooper said, later adding, "And once people are informed, I think they will hold Metro government up to a higher standard."

His decision significantly alters what many assumed would be this year's field of candidates. State. Rep. John Ray Clemmons, D-Nashville, is the only declared candidate besides Briley. Nashville real estate executive Bill Freeman is among those still weighing bids.

Freeman, who commended Cooper for being a budget hawk on the council, said he would make a decision on whether he'll run for mayor over the next four or five days.

"It certainly opens the race up," Freeman said of Cooper's move.

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Cooper on why he likely won't run for re-election

Cooper said his personal health — he had bypass heart surgery in 2015 — was not a factor in his decision.

The far more surprising move is Cooper's decision to not seek re-election as an at-large councilman "unless circumstances dramatically change." He would be heavily favored to win a second term.

He called his council service the "biggest honor of my life" and a "rich experience," but said it still takes "150 percent of your life."

"It just needs to continue for other people to do that," Cooper said. "It's a really deeply enriching experience, but it can wear you down. I would rather stay involved in the discussion of financial issues about the city and not have as many constituent service concerns."

He said there's still a lot of "legislative content" he's committed to addressing in his final term that will probably be much easier to get to without being a candidate. Cooper is not publicly endorsing any candidate for mayor at this time.

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Reach Joey Garrison at 615-259-8236, jgarrison@tennessean.com and on Twitter @joeygarrison.