What are joint fundraising committees in the campaign-finance scenario discussed in McCutcheon v. Federal Election Commission?

In the context of McCutcheon v. Federal Election Commission, joint fundraising committees are entities that collect contributions from donors and distribute those funds among several party committees.1

The district court identified these committees as a potential mechanism for evading base limits on contributions to individual candidates. The court hypothesized that a donor could make a large contribution to a joint fundraising committee, which would then distribute the money among multiple party committees in compliance with base limits. Because there are no restrictions on transfers between party committees of the same party, those committees could subsequently transfer the funds to a single party committee, which would then use the money to cover the expenditures of a specific candidate.1

While the court acknowledged it might seem unlikely for multiple entities to act as conduits for a single contributor, it noted that such a system could be used to circumvent campaign finance regulations.1