Tuesday’s special election in Georgia is the most expensive House race in history, with candidates and outside groups spending roughly $55 million in the battle for the longtime Republican-held district in suburban Atlanta.

The race to fill the United States House seat vacated by Tom Price, the new health and human services secretary, cost nearly twice the amount spent in the second-most expensive House election, which was in Florida in 2012.

Ga.-6 special Top ten most expensive House races each cycle $50 million Spending by: Outside groups Fla.-18 Candidates Calif.-50 $25 ’00 ’02 ’04 ’06 ’08 ’10 ’12 ’14 ’16 Ga.-6 special Top ten most expensive House races each cycle $50 million Spending by: Outside groups Fla.-18 Candidates Calif.-50 $25 ’00 ’02 ’04 ’06 ’08 ’10 ’12 ’14 ’16 Top ten most expensive House races each cycle Ga.-6 special Spending by: $50 million Outside groups Candidates Fla.-18 Calif.-50 $25 ’00 ’02 ’04 ’06 ’08 ’10 ’12 ’14 ’16

Sheila Krumholz, the executive director of the Center for Responsive Politics, said that the number is especially striking because the campaign has only lasted a few short months. But she also acknowledged that the race has become a referendum on the Trump administration.

“There are other forces at work here beyond Georgia,” she said.

The Democrat Received Significant Out-of-State Support

Jon Ossoff, a Democrat, and Karen Handel, a Republican, both advanced to a runoff after securing the top spots in the initial vote this April. Their campaigns raised about $28 million, with the bulk going to Mr. Ossoff.

Total raised by the campaigns Jon Ossoff $23.6 million Dem. $4.5 Karen Handel Rep. Jon Ossoff $23.6 million Dem. $4.5 Karen Handel Rep. Jon Ossoff Dem. $23.6 million Karen Handel Rep. $4.5 As of May 31.

These donors are disclosed only when their contributions are “itemized” in campaign finance filings, which generally means that donors gave at least $200.

Most of the itemized contributions to Mr. Ossoff were from large Democratic states like California and New York. Just 14 percent came from Georgia, compared with 56 percent of Ms. Handel’s contributions. Among open-seat House candidates who raised at least $100,000 in 2016, the median in-state percentage of contributions was 82 percent.

Where individual donations came from States won by: Trump Clinton Jon Ossoff $8.0m Calif. N.Y. Mass. Ga. Dem. Ill. Karen Handel $2.1m Ga. Rep. Calif. States won by: Trump Clinton Jon Ossoff Dem. $8.0m Calif. N.Y. Mass. Ga. Ill. Karen Handel Rep. $2.1m Ga. Calif. Jon Ossoff Dem. $8.0m Calif. N.Y. Ga. Karen Handel Rep. States won by: Ga. $2.1m Trump Clinton Calif. As of May 31. Data shows only itemized contributions, generally from donors giving $200 or more.

“Ossoff is a huge outlier, as far as open-seat candidates go, for out of state support,” said Mrs. Krumholz.

But the Republican Also Benefited From Outside Money

Although Mr. Ossoff’s campaign far outraised Ms. Handel’s, she had much more outside support from party committees and “super PACs.” These groups spent more than $25 million on the race, primarily on advertising against the other side.

An Atlanta television station added a 7 p.m. newscast to profit from the deluge of ads in the race.

Spending by independent groups for each candidate Democratic Congressional Campaign Committee Other groups Jon Ossoff $7.6m Dem. 5.0 2.6 Karen Handel $18.2m 6.2 6.0 6.0 Rep. Congressional Leadership Fund National Republican Congressional Committee Other groups Jon Ossoff Dem. 5.0 2.6 $7.6m Democratic Congressional Campaign Committee Other groups Karen Handel Rep. 6.2 6.0 6.0 $18.2m Congressional Leadership Fund National Republican Congressional Committee Other Jon Ossoff Dem. $7.6m 5.0 2.6 Democratic Congressional Campaign Committee Other groups Karen Handel Rep. $18.2m 6.2 6.0 6.0 Congressional Leadership Fund National Republican Congressional Committee Other As of June 19.

Most independent groups raise money from individuals, corporations and other political committees from across the country, so they are also not receiving the bulk of their support from Georgia.

The Congressional Leadership Fund, a super PAC that supports Republican House candidates, spent more than $6 million in favor of Ms. Handel. The organization’s top donors include Steven A. Cohen, a billionaire investor; Paul L. Foster, a Texas oil refiner; and the American Action Network, a group with nonprofit status that is not required to disclose its donors.