Representative Angie Craig has benefited from nearly $10 million in spending from groups whose donors remain hidden, giving her an advantage in her Senate primary against Lt. Gov. Peggy Flanagan. This influx of undisclosed money has allowed Craig to outpace Flanagan in advertising and campaign infrastructure, even as both candidates vie for the Minnesota Democratic nomination to succeed an open seat.

Flanagan, for her part, has emphasized public financing and small-dollar donations, but has struggled to match Craig's financial firepower. The primary, one of the most watched in the cycle, highlights the growing influence of dark money in intraparty contests.