Facing a threat from his left flank, Representative Kurt Schrader of Oregon wanted to send an urgent message to allies ahead of his upcoming primary: It was time to go on the attack.
The challenge: Campaign finance rules bar candidates from directly coordinating with the very outside groups that Mr. Schrader, a top moderate in Congress, needed to alert. So instead, he used a little red box.
On April 29, Mr. Schrader issued a not-quite-private directive inside a red-bordered box on an obscure corner of his website, sketching out a three-pronged takedown of what he called his “toxic” challenger, Jamie McLeod-Skinner — helpfully including a link to a two-page, opposition-research document about her tenure as a city manager.
The message was received.
On May 3, a super PAC that has…