Campaigns, political parties and outside groups have booked or aired more than $1 billion in television advertising, months before voters head to the polls in November in what is likely to become the most expensive midterm election campaign in U.S. history.

In the fight for control of the U.S. Senate, where Republicans hold a narrow two-seat majority, the two sides have already spent a combined $170 million on television spots, according to an observer keeping close tabs on the advertising market.

ADVERTISEMENT

The parties have another $230 million in airtime booked in key Senate races.

Democrats hoping to win back control of the House have aired or booked more than $135 million in television airtime, while Republicans playing defense have spent or reserved $146 million, numbers that will almost certainly increase as prominent outside groups raise and spend more money.

And the two sides have reserved a whopping $340 million in airtime in gubernatorial races across the country. The majority of that money, $250 million, has already been spent on advertisements ahead of key primary elections, hinting at an ad onslaught set to heat up in the weeks after Labor Day.

“These numbers, volume-wise, suggest we might see a record number of ads this time,” said Mike Franz, co-director of the Wesleyan Media Project, which keeps track of television advertising in political races. “There are a lot of ads on TV.”

All told, federal campaigns have spent about $1.6 billion so far this year, according to a running tally maintained by the Center for Responsive Politics. That figure takes into account spending on staff, fundraising, administrative costs and other necessities of running a modern race.

Those figures do not include gubernatorial races, which do not have to file campaign finance reports with the Federal Election Commission.

ADVERTISEMENT

They also do not include what is expected to be an influx of cash from outside billionaires like Charles and David Koch's network, which has made only initial forays into the field on behalf of some Republican candidates, or from former New York City Mayor Michael Bloomberg, who has said he will spend up to $80 million trying to elect Democrats to Congress.

100 DAYS TO MIDTERMS COVERAGE

Parties face excited midterm electorate with reservations

GOP worries trade wars will last as Trump engages in temporary tiffs

Dems have midterm edge, but it's not historic

Campaigns tend to stockpile money for a late push, meaning that total spending is likely to skyrocket in the final 100-day sprint to November. This year’s contests are likely to cost more than in 2014, which remains the most expensive midterm elections ever after federal candidates and outside groups spent $3.8 billion to influence voters.

“The trend is generally upward over time,” said Douglas Weber, a senior researcher at the Center for Responsive Politics. Weber said an influx of candidates — Democrats have seen a record number of candidates filing and running for office — account for much of the extra spending.

“If you get more candidates who are running, more activity on both sides, and you have incumbents who are spending more to defend themselves,” Weber said.

Both Democrats and Republicans are warily watching their opponents, fearful that an influx of money could skew races and swamp candidates who cannot compete with unlimited spending from outside groups.

“Democrat money and voter intensity are the greatest concerns,” said Brian O. Walsh, who runs an umbrella organization for Republican groups and is close to the White House.

Outside spending has increasingly come to dominate the campaign conversation, Weber said. This year, the Senate Majority PAC — the largest super PAC backing Senate Democratic candidates — accounts for about one in every 10 dollars spent or reserved on airtime. The group has booked more than $102 million in airtime in competitive states across the country.

On the Republican side, the Senate Leadership Fund and One Nation PAC, both groups tied to Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellTrump 'no longer angry' at Romney because of Supreme Court stance On The Money: Anxious Democrats push for vote on COVID-19 aid | Pelosi, Mnuchin ready to restart talks | Weekly jobless claims increase | Senate treads close to shutdown deadline The Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power MORE (R-Ky.), have spent or reserved a combined $67 million on television time.

One measure of how prominent outside groups have become is evident in the battle for control of the House. Super PACs backing both parties — the House Majority PAC on the left, the Congressional Leadership Fund on the right — have reserved more airtime than the Democratic and Republican congressional campaign committees.

In the Senate, both outside groups have spent multiples more on airtime than either the Democratic or Republican senatorial committees, too.

In the race to win governorships, two wealthy individuals stand out. Venture capitalist and philanthropist J.B. Pritzker, heir to the Hyatt Hotel fortune, has spent nearly $25 million on airtime so far, part of the more than $100 million he has contributed to his own campaign. His opponent, Illinois Gov. Bruce Rauner (R), also a venture capitalist, has spent $19 million on his own television ads, and tens of millions more on his bid for a second term.