From Malcolm Gladwell, an apparently otherwise intelligent human being:
When Doris Kearns Goodwin borrowed, without attribution, from a history of the Kennedys for her history of the Kennedys, that's serious. She's a scholar. And we have an expection of scholarship that it is supposed to reflect original thought. We have no such expection for genre novels, Harlequin romances, slasher films, pornos, or, say, the diaries of teenagers.
It is worth reading, I think, the actual passages that Viswanathan is supposed to have taken from McCafferty. Let's just say this isn't the first twenty lines of Paradise Lost.
Calling this plagiarism is the equivalent of crying "copy" in a crowded Kinkos.