Ken Doyle for Bloomberg (I miss his daily Money & Politics report in my inbox):

“Shadow parties,” outside groups allied with Democratic and Republican leaders, are eclipsing traditional political parties, according to two new studies of campaign spending in the 2018 midterm elections.

The reason is simple: groups not formally tied to candidates can raise more money under current campaign finance rules.

The shadow parties rely almost exclusively on megadonors giving at least $100,000 each or on undisclosed donors, researchers found.

“Presumably, the party leaders raising the money know where it comes from,” said Ian Vandewalker, the author of one of the studies, which was released by the Brennan Center for Justice at New York University Law School.

Super political action committees and other groups aligned with top Democratic and Republican leaders in the House and Senate have become the predominant campaign money source in the current midterms, outraising the traditional party committees they’re assisting in three of four instances, the Brennan Center found.