A release from the Campaign Finance Institute:
General Election IE Tool
Independent expenditures (IEs) reported to the Federal Election Commission (FEC) for general election House and Senate contests have continued on a record pace, totaling $695 million through October 21st. This is $103 million more than on the same date in 2016, based on a Campaign Finance Institute (CFI) analysis of data supplied by the FEC. Detailed data on all races with independent expenditures, and on the organizations making the IEs, are available and updated daily on CFI's website via these links: House | Senate |Spenders.
Eight of the top ten spenders in the general election are party committees (DCCC, NRCC, NRSC, DSCC) or organizations, mostly Super PACs, tied to the congressional leadership. These organizations were responsible for a combined $409 million, or 59% of all general election IEs through October 21. Breaking them down, the leadership-related entities have been responsible for $265 million and the formal party committees $144 million. This is the first time the leadership-related committees have been quite so important. In 2014 the leadership-related groups spent about half as much as the formal party committees. By 2016 they had pulled almost even. This year, the leadership-related entities so far have come close to doubling the formal party committees.
With respect to the partisan breakdown: All IE spending has been virtually even in the amount spent to support Democrats and Republicans. Republican candidates currently hold a slight edge at 51% to 49%.
A large number of House races are considered to be competitive this year and IE spending decisions are backing that up. In 2016 there were forty House races that had $1 million or more in independent expenditures through the entire general election. With two weeks still remaining before the 2018 election, there are already sixty-two districts with over $1 million in outside money.
The competitive landscape in the House is heavily weighted towards Republican incumbents defending their seats. The top ten House races by IE spending, each exceeding $9 million, all represent such districts. On the Senate side, the situation is mostly reversed with Democrats defending seats in seven of the top ten races.