Mark Liberman's post at Language Log about the minor furor over plagiarism in work published under Sen. Rand Paul's name, along with some of the comments, allows us to make some useful distinctions. What counts as plagiarism, passing off someone else's work as one's own, differs according to context. 
In the academic context, copying ideas or verbatim text without citation, or purchasing papers,* appropriating another person's work, is unforgivable, because the point of an academic paper is not publication but a demonstration that the writer can master the subject and the requisite analytical skills. 
In the political and corporate context, however, using the work of other people under one's name is not a problem, because it is commonly understood, except perhaps among the completely unsophisticated, that staff members are doing research and drafting texts.
Presidents of the United States have openly employed speechwriters for decades, and few, I think, would imagine that many corporate chief executives could produce a book unassisted.  
What has gotten Senator Paul in Dutch is the second element of plagiarism: the unacknowledged appropriation of verbatim language.** His staff evidently copied from Wikipedia (Wikipedia!) and other published sources, the number of which increased as scrutiny intensified. 
Growing tetchy about the subject, Senator Paul told The New York Times“What we are going to do from here forward, if it will make people leave me the hell alone, is we’re going to do them like college papers.”
Senator Paul has evidently been badly served by his staff, members of which appear not to have a proper grasp of the conventions. And not only the political conventions but the academic ones; cribbing from an encyclopedia (and an unreliable one at that) is not something that one would expect to see beyond high school.
For a United States senator, particulaly one thought to display presidential ambitions, this is embarrassingly amateurish. 
The ethical principles involved in cases of plagiarism and fabrication are not arcane. They can be summed up in two sentences you probably heard in elementary school: Don't copy. Don't tell lies.
*The Chronicle of Higher Education's 2010 article, "The Shadow Scholar," is illuminating about the widespread practice.
**A bipartisan phenomenon. You will recall that in his ill-fated presidential campaign in 1987, Sen. Joe Biden got caught appropriating verbatim language from a speech by British Labour Party leader Neil Kinnock.