It’s sometimes said journalism is the business of making mistakes in public.

The Milwaukee Journal Sentinel knows what that’s like, as it made a whopper of a mistake on its front page Tuesday. In an above-the-fold story by three of its top reporters, the paper reported allegations that Gov. Scott Walker’s “campaign crossed a bright legal line by coordinating with independent conservative groups that expressly called for the election of specific candidates in the recall elections for governor and state Senate in 2011 and 2012.”

The Journal Sentinel’s description of the law is simply wrong, and if its reporters had checked the dates of the emails they were reporting on, they’d have noticed a little problem: they date from seven months before the Walker recall campaign existed. Whatever the merits of the legal theories at issue, the reporters ought to admit there’d be certain difficulties in coordinating with non-entities.