A week before the Nov. 6 election, Kendra Horn, a Democratic House candidate in Oklahoma, received unexpected good news from her television consultant: Michael R. Bloomberg’s political action committee, a leading supporter of Democratic candidates, had purchased more than $400,000 in advertising on Oklahoma City television.
Still, Ms. Horn’s campaign did not realize just how big a boost it was receiving. The ad was not just a general get-out-the-vote message supporting Democrats, as they had assumed. Instead it attacked her Republican opponent, the incumbent Steve Russell, on his education record.
Ms. Horn’s campaign manager, Ward Curtin, said that once they saw the ad, “Obviously, we recognized it was a big deal.”
With just days to go before the election, and Ms. Horn fighting an uphill battle in a deeply conservative state, Mr. Bloomberg’s group had effectively doubled the television spending on her behalf, catching Mr. Russell flat-footed and unable to respond.
Ms. Horn, who had trailed in both a local poll and in Mr. Bloomberg’s internal polling, won by 3,338 votes.
Big donors like the Adelsons, the Uihleins, the Koch brothers on the Republican side and Tom Steyer and George Soros on the Democratic side have become integral and influential players in every election cycle. But in this year’s midterm elections, Mr. Bloomberg, the former mayor of New York, emerged as a powerful and effective force, as well as the biggest outside spender promoting Democratic House candidates, according to disclosures filed with the Federal Election Commission.
Records filed so far show that organizations controlled and funded by Mr. Bloomberg spent more than $41 million on 24 House races, much of it on eye-catching ads rolled out on social media and broadcast on television in the crucial final days of the campaign.
And while it’s impossible to conclude that any one factor tipped the balance in a race, Mr. Bloomberg appears to have reaped the benefits of his millions in giving. Democrats won 21 of the 24 races he sought to influence. Of those, 12 had been considered either tossups or in Republican districts.
“The mission was to flip the House. Success or failure would be defined by that,” said Howard Wolfson, a senior adviser to Mr. Bloomberg.
Assessing the election outcome, Kevin McCarthy, the House Republican leader, cited Mr. Bloomberg’s spending as a significant factor. “Michael Bloomberg’s money went a long way. He defeated a lot of people by writing those $5 million checks,” Mr. McCarthy told CNBC.
Kyle Kondik, managing editor of Sabato’s Crystal Ball at the University of Virginia Center for Politics, credited Mr. Bloomberg’s operation for picking smart races.
“I don’t think you could say they were the difference between the Democrats winning and losing the majority,” Mr. Kondik said, “however I think you could say that Mr. Bloomberg and his late money may have made a difference in a few of the surprising results that helped pad the size of the Democratic majority.” He pointed to Ms. Horn’s campaign as an example.
Mr. Bloomberg, who first ran for New York mayor as a Republican but recently registered as a Democrat, is considering his own run for the White House in 2020. He is scheduled to appear in Iowa, the first presidential caucus state, on Tuesday to host a premiere of a new documentary.
Mr. Bloomberg’s organization in many ways mirrors the Senate and House majority PACs that raise and spend money to support individual candidates, focusing on close and winnable races. But his operation has advantages over most other political groups, including these big party-affiliated committees, that make it easier to more effectively deploy its money.
Because his PACs are funded by his personal wealth, they don’t rely solely on outside donors, they don’t have to spend time raising money and they know exactly how much cash will be on hand at a given time, meaning they can time their spending — specifically ad purchases.
When the final reports are filed next month, Mr. Bloomberg’s organization says they will show that the former mayor and his organizations spent $44 million on television ads and another $12 million on digital advertising in support of House candidates. Overall spending by Mr. Bloomberg and his organizations in the 2018 elections topped $112 million, an amount that also includes donations to help Senate candidates and progressive organizations.
That puts him on the same level as Sheldon and Miriam Adelson, longtime Republican megadonors who had given $112 million to Republican Super PACs as of Oct. 17.
His political giving often aligns with issues like gun control and climate change that are the focus of his two PACs — Everytown for Gun Safety and Independence USA.
In a recent interview at the New York headquarters of Bloomberg Philanthropies, Mr. Wolfson and other staff members described their House election strategy, which involved spending on digital advertising beginning in September and spending “big” and “late” on television advertising. Records show that more than $30 million of Mr. Bloomberg’s spending on House races came after Oct. 22.
“I had a budget,’’ Mr. Wolfson said. “It was a big budget. I didn’t have to raise it. I knew it was coming and that gave us real advantages in terms of spending late in these expensive markets. We were able to really come in and overwhelm at the last minute in some of these places.”
The group identified target districts based on a theory that highly educated voters were more likely to vote Democratic, even if they had previously voted Republican. Mr. Bloomberg’s operation hired two companies that analyzed educational achievement in Republican congressional districts, Mr. Wolfson said.
They identified districts previously ignored by national Democrats where there were opportunities to stretch the Democratic map.
One of those was Oklahoma’s 5th Congressional District, where an increasingly young and well-educated electorate had been lured by jobs and the urban conveniences of Oklahoma City, and where Mr. Horn was running.
Ten days before the election, polling commissioned by Mr. Bloomberg’s organization showed Ms. Horn trailing by five points. There had been little outside spending in the campaign. Advertising in the Oklahoma City market is relatively inexpensive.
“The conditions seemed to suggest opportunity,” Mr. Wolfson said.
The ad released just days before the election called Mr. Russell “part of the mess” that led to the low ranking of Oklahoma’s schools — 49th in the nation.
Local media emphasized that the ad aired during halftime of the closely-watched University of Oklahoma football game. In fact, the Bloomberg team had blanketed local television. “We bought so many ads in such a short period of time, it was running at halftime, quarter time, three-quarter time and postgame,” Mr. Wolfson said.
Another avenue for Mr. Bloomberg’s groups is digital advertising, which Mr. Wolfson compares to doing previews off Broadway. Digital ads are cheaper and carry metrics showing how many people clicked, how long they watched and how many people shared. Using those metrics, Mr. Bloomberg’s operation was able to identify successful digital ads that they could move to television.
An ad in California’s 48th District, first rolled out on digital platforms, targeted the 15-term incumbent Dana Rohrabacher. Against a backdrop of raging California wildfires, Mr. Rohrabacher says, “Global Warming is a Fraud.” Already a vulnerable candidate because of his perceived close ties to Russia, Mr. Rohrabacher lost to his Democratic opponent, Harley Rouda.
It was one of three California races in which Mr. Bloomberg’s organization spent more than $10 million combined. The Democrats supported by Mr. Bloomberg won all three seats.
Health care and taxes were major themes of the Bloomberg ads. In Illinois’s 14th Congressional District, a suburban Chicago area, one Bloomberg-funded ad emphasized the Democratic challenger Lauren Underwood’s record as a registered nurse who would fight for health care.
A separate ad attacked the four-term incumbent, Randy Hultgren, for his vote in favor of the bill limiting deductions for state and local taxes, which the ad claimed would lead to “higher taxes for many Chicagoland families.”
A New York Times Upshot/Siena College poll a month before the election showed Ms. Underwood trailing Mr. Hultgren; she won by 10,442 votes.
In Houston, a media market saturated with political advertising, one ad stood out for its quirkiness. It featured a cartoonlike depiction of the Republican incumbent, Representative John Culberson, riding a spaceship.
Mr. Culberson had pushed millions of dollars in funding for a NASA mission to find signs of life on Jupiter’s moon Europa.
“John Culberson: Out of this World,” the ad trumpeted.
The message dovetailed with criticism leveled by Mr. Culberson’s Democratic opponent, Lizzie Fletcher, that he had failed to secure proper funding for Houston flood control, showing misplaced priorities.
“It was definitely the most-talked-about ad in the Houston area,” said Tony Essalih, a former aide to Mr. Culberson and now a principal with Cornerstone Government Affairs, a lobbying firm. “In terms of driving up his negatives, I think it had an impact.”
Ms. Fletcher, who had trailed before the election in both the Bloomberg internal polling and the Times Upshot/Siena College poll, won by about 12,000 votes.