With just over a week until voting day, the records in the notoriously expensive US election system have been shattered.
An AFP news agency analysis of federal data shows just five groups known as super PACs (political action committees) accounted for nearly a third of non-party spending in this election cycle as of October 25.
Significantly funded by dark money, they have poured more than $1 billion into the US midterm election campaign.
Three of the five groups skew Republican, and about two thirds of the billion dollars spent will benefit the Republican Party (GOP), fuelled by ultra-wealthy Republican-leaning donors like Elon Musk — a key ally of President Donald Trump.
Musk alone has put almost $450 million into Republican groups, including the biggest of the super PACs, the Senate Leadership Fund.
Meanwhile, Democrats have a fundraising edge when it comes to direct donations to candidates' campaigns and to the party's national committees.
Democratic candidates in competitive Senate and House races have consistently outraised their Republican counterparts.
That suggests smaller donors in the Democratic base are highly motivated.
But tortuous US election laws impose strict caps on how much individuals can give, while there is no limit — or really any control at all — on how much super PAC groups can throw at candidates.
Unlimited contributions
The six giant spenders in this cycle are technically a mix of super PACs and hybrid PACs, entities that didn't even exist before 2010.
They grew out of a Supreme Court ruling, known as Citizens United, which held that the government cannot limit political spending by corporations, unions and other groups if they spend it independently of candidates.
A lower court decision ruled that these organisations could also raise an unlimited amount of money from donors.
The result was that big donors can funnel vast sums of money to try and influence elections and remain anonymous by donating through secondary organisations.
In contrast, direct contributions to a candidate's official campaign are limited to a mere $3,500, and donations to national party committees have a cap of $44,300.
The PAC spending sprees have surged ever higher during the Trump era, with Musk's mega-million donations encapsulating the new reality of pay-to-play politics.
Across the nation, super PACs have put far more of their money into Senate contests and spent it largely on attack ads.
The Texas Senate election tops the list in terms of expenditure. Democrat James Talarico has faced more than $200 million in opposition from outside spending groups as he attempts to become the first Democrat to win a Senate race in Texas since 1988.
Second is Ohio's special Senate election, where Democrat Sherrod Brown has also faced extensive outside spending against him — nearly $170 million — as he tries to return to the Senate.
