More than $2.5 million has been spent in the Honolulu mayoral campaign since the Aug. 13 primary election, about half of it from independent political action committees seeking to sway voters both for and against incumbent Mayor Kirk Caldwell.

Caldwell has outspent challenger Charles Djou by a 3-to-1 margin since the primary, according to reports required to be filed Monday with the Campaign Spending Commission.

Caldwell for Mayor reported spending $947,549 from Aug. 14 to Oct. 24. Djou for Mayor reported spending $339,728 during that same period.

Caldwell collected $565,994 during that span, more than double the $263,040 that Djou raised during the same period. The Caldwell campaign reported $118,309 cash on hand going into the final stretch of the election while the Djou camp reported $72,086.

Overall, Djou has raised an impressive $920,337 in the nearly five months since announcing his challenge to Caldwell on June 7. But the mayor began 2016 with $1.6 million already in his campaign war chest, and as of Oct. 24 had amassed $3,498,844, more than three times that amassed by Djou.

Political action committees — both of the “super PAC” and traditional PAC variety — have meanwhile inundated potential voters with more than $1.5 million in broadcast, print and internet advertising, as well as mailers.

Super PAC Workers for a Better Hawaii topped the field, spending $572,268 since the primary from Aug. 14 to Oct. 24 on advertising both in support of Caldwell and in opposition to Djou, as well as surveying and mailing.

Newly required electioneering communication reports show Workers for a Better Hawaii spent more than $750,000 through Oct. 31.

A super PAC can collect and spend unlimited amounts of money, so long as there is no communication between the committee and the candidate.

The pro-Caldwell Workers for a Better Hawaii is getting money from the Hawaii Government Employees Association as well as fellow union organizations Hawaii State AFL-CIO, AFSCME and the Hawaii Regional Council of Carpenters. The Hawaii Regional Council of Carpenters was the key backer of the Pacific Resource Partnership. In 2012 the now-defunct PRP super PAC waged the controversial $3.6 million advertising campaign against Gov. Ben Cayetano’s mayoral bid. Cayetano sued the PAC for defamation, which was settled when PRP agreed to issue a public apology and donate $125,000 to two charities.

Meanwhile a group calling itself Save Our City LLC said in its report that it spent $274,595 through Oct. 26 in an advertising campaign aimed at getting voters to reject Caldwell. Super PAC organizer Sarah Houghtailing, a business owner, told the Honolulu Star-Advertiser last week that her group would spend about $300,000 on its campaign.

Save Our City’s report showed that $170,000 of its funding, more than half, came from Dennis Mitsunaga, president of local architectural, engineering and construction management firm Mitsunaga and Associates. An additional $36,490 was contributed by 11 Mitsunaga officers and employees.

Mitsunaga, a longtime supporter of Cayetano and other elected officials, said in an email to media Tuesday that he wanted to help his friend Houghtailing, who is frustrated with Caldwell’s missteps with the $8 billion rail project. Mitsunaga said he supports rail but that the incumbent is “unqualified and unfit” to deal with rail and other issues.

Mitsunaga noted unions are supporting Caldwell through large amounts of advertising. He also said he knew Houghtailing would “be fighting an uphill battled against the biased media.”

Djou told reporters Tuesday that he denounces all super PAC money, including that targeted to support him or oppose Caldwell, and that the public should ignore super PACs. “They are a distraction from the underlying issues here in this mayor’s campaign,” he said.

The third-party groups, allowed by the U.S. Supreme Court under the so-called Citizens United decision, “are bringing up issues that have nothing to do with the mayor’s campaign,” he said. “And so whether these third-party ads are supporting me or opposing me, I condemn all of them.”

Caldwell did not go so far as to condemn all super-PAC funding, but said he objects to efforts that focus on personal attacks. “I’m OK when they talk about issues of record — of how we vote. I get more trouble when it’s just outright, negative character attacks,” he said.

Without mentioning Save Our City by name, Caldwell said he is concerned by super PAC ads that do not clearly identify who is producing them. Save Our City has been running ads for several weeks but, until yesterday’s spending report was submitted on deadline, had not disclosed the source of its funding. “In some cases it’s pretty shadowy. … Now, I don’t like that at all.”

The PACs that support him are largely made up of unions that clearly explain who they are and why they support him, he said.

At dueling press conferences by the two candidates Tuesday:

>> The Sierra Club Oahu Chapter and state chapter announced its support of Caldwell. Anthony Aalto, chapter president, said the mayor’s willingness to work with the group and his support of a charter amendment creating an Office of Climate Change were key reasons for its decision. Djou said he believes climate change issues can be addressed without creating new bureaucracy. Aalto acknowledged that the group has had strong differences with Caldwell and that other environmentalists might disagree with the club’s decision.

>> Djou outlined a 100-day plan as mayor. “Six words, three promises: Fix rail, reduce homelessness, restore ethics,” he said. “The people will see a real profound and clear difference in the City and County of Honolulu within the first 100 days after I get elected.”