The real point of the phrase “man bites dog” is to suggest that journalists have a bias toward surprising news, even if it’s merely anecdotal. But these days, that’s often at best a half-truth, which is often the most effective kind of whole lie. When it comes to politics, what ignites the press isn’t surprise but confirmation. The great herd stampedes when it hears what it expects to hear. Surprises get squashed or squelched, which is why it has become a parlor game to see how long it takes wire stories about corrupt politicians to mention their party affiliation. If they are Republicans, it’s in the lede. If they’re Democrats, it’s usually ten paragraphs down, if anywhere at all.
That’s why actual dog-bites-man stories make it to the front pages, while man-bites-dog stories are negligible filler. When a Republican candidate does or says something awful, it’s a newsworthy dog-bites-man story because the press believes it is their duty to report on the true, feral nature of conservatives: “Rabid Republicans Claim Another Victim.” When a Democrat does or says something awful, it’s a curiosity, an anecdote, at best suitable for a squib in the back pages: “Local Puppy Learns to Play the Piano.”