Editor’s Note: David Mark is a political journalist, author and public speaker. He is the author of “Going Dirty: The Art of Negative Campaigning” and co-author of “Dog Whistles, Walk-Backs, and Washington Handshakes: Decoding the Jargon Slang and Bluster of American Political Speech.” The opinions expressed in this commentary are his own. Read more opinion at CNN. CNN — Recent Democratic presidents have sought reelection by limiting overt campaigning and instead making sure they’re seen focusing on the nuts and bolts of their job. President Bill Clinton, in his successful 1996 reelection bid, spent the late months of his campaign...