The fight for control of the Senate has generated more than half a billion dollars in television advertising spending as both sides focus on a handful of competitive races.

With five weeks to go before Election Day, candidates, parties and outside groups have reserved or purchased $561 million in television time across 27 states, according to sources tracking the advertising market.

ADVERTISEMENT

As Republican presidential nominee Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE struggles to raise money and attract outside allies, the fight for control of the Senate is proving more costly than the presidential race, a first in recent history. The two presidential campaigns and their outside affiliates have reserved or spent a relatively paltry $346 million on television advertising.

“It’s unusual that there would be more spending in the Senate races than the presidential race,” said Carl Forti, a Republican media strategist involved in several major outside groups. “On the Republican side, Donald Trump has chosen to run a more earned media-centered campaign, and there are not any GOP outside groups spending significant dollars.”

Democrats and Republicans are spending the lion’s share of their money in eight states that will decide whether Mitch McConnell Addison (Mitch) Mitchell McConnellGraham: GOP will confirm Trump's Supreme Court nominee before the election Trump puts Supreme Court fight at center of Ohio rally The Memo: Dems face balancing act on SCOTUS fight MORE (R-Ky.) or Charles Schumer Chuck SchumerJacobin editor: Primarying Schumer would force him to fight Trump's SCOTUS nominee CNN's Toobin: Democrats are 'wimps' who won't 'have the guts' to add Supreme Court seats Republican senator says plans to confirm justice before election 'completely consistent with the precedent' MORE (D-N.Y.) is the next majority leader. Together, those eight states — New Hampshire, Pennsylvania, Ohio, Nevada, Florida, North Carolina, Missouri and Indiana — account for $487 million in television spending.

The pitched fight between New Hampshire Sen. Kelly Ayotte Kelly Ann AyotteBottom line Bottom line Bottom Line MORE (R) and Gov. Maggie Hassan (D) is the priciest contest in the nation so far. The two sides have spent just shy of $100 million battling over a tiny handful of undecided voters. Two polls released in the last week by WBUR and Monmouth University show the candidates statistically tied, separated by just 2 percentage points.

In Pennsylvania, Democrats and Republicans have spent $90 million on advertising supporting and attacking Sen. Pat Toomey (R) and Katie McGinty (D), a former state environmental official and gubernatorial chief of staff. Three consecutive surveys show McGinty leading by a small margin.

Ohio Sen. Rob Portman Robert (Rob) Jones PortmanMcConnell locks down key GOP votes in Supreme Court fight Romney undecided on authorizing subpoenas for GOP Obama-era probes Congress needs to prioritize government digital service delivery MORE (R) leads former Gov. Ted Strickland (D) by a significant margin, but only after Republicans and Democrats spent nearly $80 million on television spots. Democratic outside groups have canceled several weeks of advertising in Ohio, a sign that Portman’s lead is unlikely to diminish.

One of the quietest races in the nation is in Nevada, where both candidates have remained largely under the radar.

Still, Rep. Joe Heck (R),

former state Attorney General Catherine Cortez Masto (D) and their outside allies have spent a combined $65 million in the fight for retiring Democratic Sen. Harry Reid Harry Mason ReidOn The Trail: Battle over Ginsburg replacement threatens to break Senate Democrats fear Russia interference could spoil bid to retake Senate Graham signals support for confirming a Supreme Court nominee this year MORE’s seat. Heck leads recent polls, though both candidates are well under 50 percent.

North Carolina Sen. Richard Burr Richard Mauze BurrRep. Mark Walker says he's been contacted about Liberty University vacancy Overnight Defense: Trump rejects major cut to military health care | Senate report says Trump campaign's Russia contacts posed 'grave' threat Senate report describes closer ties between 2016 Trump campaign, Russia MORE (R) finds himself in an unexpectedly close battle against former state Rep. Deborah Ross (D), and both Democrats and Republicans are rushing to purchase airtime in an expensive state that is also a presidential battleground. The two sides have reserved $33 million in airtime so far.

Big-spending groups like the Senate Leadership Fund, which backs Republicans, and the Democratic Senatorial Campaign Committee (DSCC) have been purchasing new advertising time in recent weeks. Two recent polls from Elon University and Bloomberg show Ross leading by statistically insignificant margins.

In Missouri, Sen. Roy Blunt Roy Dean BluntThis week: Supreme Court fight over Ginsburg's seat upends Congress's agenda McConnell locks down key GOP votes in Supreme Court fight Murkowski: Supreme Court nominee should not be taken up before election MORE (R) also faces a spirited challenge from Secretary of State Jason Kander (D). The two sides have spent $31 million on the contest, though polls show Blunt slightly ahead of Kander in a state that has trended away from Democrats in recent years.

Former Sen. Evan Bayh (D), seeking to reclaim his old Indiana Senate seat, brought a $10 million war chest to the race when he jumped in late this summer.

But Republicans believe Rep. Todd Young Todd Christopher YoungSenate GOP eyes early exit Why the US should rely more on strategy, not sanctions Davis: The Hall of Shame for GOP senators who remain silent on Donald Trump MORE can close the gap, and the GOP has spent heavily to bolster Young’s bid. In a sign of a tightening race, the DSCC has begun investing in Indiana airtime, too. The two sides have reserved $31 million in ads this year.

Candidates do not have to file updated fundraising reports until the middle of the month, but the campaigns themselves are likely to have raised and spent more than $400 million alone by the time Election Day rolls around.

Through the end of the second quarter of the year, candidates running in the 10 most expensive states had raised $262 million, according to a running tally maintained by the Center for Responsive Politics.

A large percentage of the money candidates raise will be spent on television advertising, though not all of it.

Outside groups are adding hundreds of millions in fuel to the televised fire. The DSCC has spent more money — $59.8 million — on television ads than any other group.

Michael Franz, a political scientist at Bowdoin College who tracks television ad spending, said outside groups are playing a bigger role this year than they have in previous cycles — especially because parties themselves are playing a smaller role.

“This cycle so far has seen the highest proportion [of outside spending] we’ve ever seen,” Franz said. “It’s all flowing down into the Senate races. There’s just so much extra money there that it’s just trying to find its way into the most competitive races.”

The Senate Leadership Fund, which is connected to the American Crossroads network, has spent $54.3 million. Senate Majority PAC, which supports Democratic candidates, has dropped $42.6 million on television ads this year, while the National Republican Senatorial Committee has reserved almost $40 million to date.

Other outside groups have made their presence felt as well. Granite State Solutions, a super PAC with ties to the Crossroads network that supports Ayotte in New Hampshire, has spent nearly $24 million on her behalf.

And late spending continues to pour in: In Wisconsin, where Sen. Ron Johnson Ronald (Ron) Harold JohnsonThis week: Supreme Court fight over Ginsburg's seat upends Congress's agenda GOP set to release controversial Biden report Democrats fear Russia interference could spoil bid to retake Senate MORE (R) faces an uphill battle for reelection, the Wisconsin Alliance for Reform said it would spend $365,000 this week alone on advertisements attacking former Democratic Sen. Russ Feingold’s position on late-term abortions.

The big spending on Senate races stands in contrast to earlier years, when the presidential fight was the main event.

In 2012, President Obama, Republican nominee Mitt Romney and their respective allies spent close to $1 billion on television advertising, while candidates and outside groups spent a little more than $700 million on advertisements aimed at Senate races, according to data compiled by the Wesleyan Media Project and the Center for Responsive Politics.

“Most major Republican donors are sitting this one out,” said Forti, the Republican media strategist.