Outside groups have funneled cash into key Senate races this year as the major parties fight for control, and one contest has already become the most expensive ever for a Senate seat.
Candidate committees and independent groups have spent more than $113 million on the Senate race in the key state of Pennsylvania, where incumbent Republican Pat Toomey is fighting off a challenge from Democrat Katie McGinty, according to Federal Election Commission data compiled by the Center for Responsive Politics. With two weeks to go, it has already surpassed the previous most expensive race, the 2014 North Carolina contest won by Sen. Thom Tillis.
Tight Senate races outside of Pennsylvania are also drawing huge money. More than $95 million has already been spent in the New Hampshire contest pitting incumbent Kelly Ayotte against the state's Gov. Maggie Hassan. At least $83 million has been spent in the Nevada race featuring Republican Joe Heck and Democrat Catherine Cortez Masto.
The spending in these key race underscores the growing power of independent groups and political action committees as the Republicans and Democrats fight for control of the Senate. Some of those groups are not subject to the contribution limits facing campaign committees.