Denver runoff between Mike Johnston, Kelly Brough has yet to hit traditional muddy patch | TRAIL MIX

Brace yourself.

Ballots go out in a matter of days for Denver's mayoral runoff, and it's a safe bet that at least a smidgeon of mud will start to hit the fan as ballots begin hitting voters' mailboxes.

Since none of the 16 first-round candidates won a majority of the vote in the April 4 election, the top two finishers — former state Sen. Mike Johnston and former chamber of commerce chief Kelly Brough — face off in the final round, with ballots due on June 6.

It's the first race for an open seat in a dozen years, since term-limited Mayor Michael Hancock won the first of his three elections.

Partly for that reason — there's no margin in gaining a reputation as the attack dog in a crowded field when the object is to motivate enough of your supporters to make the runoff — the candidates mostly treated each other respectfully in the first stage of the campaign. After all, the pair of runoff-bound survivors didn't get enough votes to win outright, so have to win over voters who backed their former rivals, a difficult proposition if their attacks kept a voter's favorite from advancing.

That isn't to say the first round was all sunshine and rainbows. Several candidates who fell short in April came under heavy criticism for their positions or their personalities, though the attacks largely played out in the press and not between the candidates, who sometimes vehemently disagreed but kept the discussion mostly on the issues.

So far, with only a couple of passing hiccups, the city has been treated to remarkably clean campaigns in the runoff, as Johnston and Brough make their respective cases to voters, racking up endorsements and organizing volunteers for what's sure to be a massive turnout effort by both camps.

The candidates and their crews have vowed to stick to the high road — Brough even requires that members of her campaign team sign a clean campaign pledge — but the outside groups supporting Brough and Johnston are under no such obligation. That'll probably be the source of any attacks that emerge.

About those hiccups.

Early in the runoff, just days after the match-up was finalized, Johnston took what Brough's staffers viewed as a swipe at their candidate in a fundraising letter, where he noted that she had a history of advocating for conservative positions over the years when she ran the chamber of commerce, including opposition to mandated family and medical leave and against raising the minimum wage.

In response, Brough's campaign fired off an email to her supporters blasting Johnston for "already launch[ing] a negative campaign attack against Kelly" and lobbed some attacks of their own while they were at it. Repeatedly calling Johnston a "career politician," Brough's campaign manager termed it "extremely disappointing" — but not surprising — that the candidate backed by wealthy, out-of-state donors was dragging the race into the mud so soon.

Days passed without either campaign escalating the attacks, though both sides professed they were merely laying out contrasts between the two candidates denied they'd gone negative.

The initial, stalled attacks were relatively mild. It's no secret Johnston has held office and made unsuccessful runs for governor and U.S. senator with support from Silicon Valley, nor is Brough's experience as head of the city's most prominent business group something she downplays. But it could offer previews of the mud to come if the campaign turns negative.

Both Johnston and Brough are Democrats — likely a prerequisite in a city where Joe Biden won 80% of the vote against Donald Trump — and each has gotten crosswise with key Democratic constituencies during their years in the public spotlight.

Johnston, a former teacher and school principal, drew the ire of teachers unions early in his stint at the statehouse when he sponsored legislation to hold teachers accountable for their students' performance on standardized tests, situating himself on the reform side in an ongoing battle over public education.

Likewise, Brough's dozen years championing business-friendly positions leaves her vulnerable, with a record of public pronouncements often at odds with prevailing voter sentiment, even though she protests she was simply doing her job and doesn't hold many of the positions she espoused.

There's no guarantee this year's runoff will descend into attacks. It's possible the candidates and the outside groups supporting them will focus on the candidate's qualifications and their proposals to confront the burning issues facing the city.

In the city's 10 previous municipal elections, Denver voters have only chosen the next mayor three times without sending the contest to a runoff — Wellington Webb's third-term win in 1999, John Hickenlooper's successful run for a second term in 2007, and Hancock's cruise to a second term in 2015.

But while the runoffs that resulted were often heated — the finalists are vying for what's arguably the most powerful elected position in the state — there's no hard and fast rule that the campaigns have to veer into the gutter.

Of Denver's seven mayoral runoffs in the last 40 years, three stand as models of positive campaigning on both sides: in 1983, when Federico Peña, a young state lawmaker, beat Dale Tooley, the district attorney; in 1991, when Webb, a former state lawmaker and the city's auditor, beat Norm Early, the district attorney; and in 2003, when brewpub owner Hickenlooper beat Denver Auditor Don Mares.

The other four runoffs, however, took decidedly negative turns, leading voters to shake their heads at the spectacle — politicians! what do you expect? — and leaving the eventual winner spattered with dirt.

Peña had a rocky run for a second term in 1987, when 17th Street lawyer Don Bain — the last Republican to make it to a mayoral runoff in Denver — unfurled a series of blistering attacks, charging the incumbent with being out of touch and not up to the job. Webb faced charges of cronyism in his bid for a second term in 1995 from challenger Mary DeGroot, a former councilwoman, who also blasted the mayor for delays opening Denver International Airport.

It was during Hancock's first and third runs for mayor in 2011 and 2019, however, that Denver voters were witness to modern heights of mudslinging.

In his first race, Hancock, a councilman, mostly smiled and shrugged off a steady stream of attacks from his opponent for the open seat, former state Sen. Chris Romer, and his zealous supporters.

At one point, a shadowy outside group flooded mailboxes with postcards featuring dinosaur skeletons and a message alleging that Hancock "doesn't believe in evolution," after Hancock appeared to say in a debate that he thought creationism should be taught in public schools, though Hancock protested that he'd misunderstood the question.

Near the end of the campaign, former U.S. Rep. Tom Tancredo, the polarizing Jefferson County Republican, said he admired Hancock's life story, and Romer's supporters promptly turned the remarks into an attack on their rival. An amused Tancredo responded by facetiously endorsing Romer, proclaiming "Viva Romer!" in a sound bite that got heavy play on conservative talk radio stations.

Hancock's win over urban planner Jamie Giellis for a his current term four years ago was nasty from the get-go, with both candidates comparing each other to Donald Trump at different points amid hurling attacks nearly nonstop at each other.

Giellis accused Hancock of fostering a "culture of sexual harassment" at city hall, saddling the incumbent with a series of harassment and sexual misconduct settlements by the city during his administration, bolstered by Hancock's apology for sending inappropriate, sexually charged text messages to a member of his security detail years earlier.

In return, Hancock's campaign accused Giellis of lacking racial sensitivity — all but branding the political newcomer a racist — after she couldn't says what the initials NAACP stand for in an interview and amped up the pressure when a decade-old social media post by Giellis wondering why "so many cities feel it necessary to have a 'Chinatown'" surfaced.

Ernest Luning has covered politics for Colorado Politics and its predecessor publication, The Colorado Statesman, since 2009. He's analyzed the exploits, foibles and history of state campaigns and politicians since 2018 in the weekly Trail Mix column.

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