On Monday, Hillary Clinton's campaign rolled out a new line of attack against Barack Obama, accusing him of plagiarism for lines he delivered in a recent speech that bore a distinct similarity to words Massachusetts Gov. Deval Patrick used in his election campaign in 2006. (A video sent out by the Clinton campaign comparing Patrick's and Obama's remarks is at the end of this post.)

Apparently, the Clinton campaign considers this an important charge -- at least, important enough that it isn't just being made by surrogates. Speaking to reporters Monday night, the candidate herself said, "Facts are important. I'm a facts person. If your whole candidacy is based on words, it should be your own words."

It's a tricky accusation to make in a political campaign. Clearly, plagiarism can have a negative -- even fatal -- impact on a presidential campaign. Just ask Sen. Joe Biden, D-Del., whose 1988 run was torpedoed in part by revelations that he borrowed parts of a British politician's speech without attribution. But at the same time, political rhetoric is rarely, if ever, wholly original. (Indeed, the remarks in question are mostly just quotes of famous lines from previous eras.) As Marc Ambinder observed,

Using the standard that finds an objection in what Obama did, every politician owes residuals to the corps of political pollsters who created the library of platitudinous phrases that so often comprise the average stump speech. "In the end, it's about the children." "This election is about the future, not the past."

The best speakers tend to appropriate and expand; Obama's speeches pay tribute to the entire Kennedy family (and to the Sorensenian/Shrumian influences on their rhetoric); to Martin Luther King and to Barbara Jordan ("Are we to be one people bound together by common spirit, sharing in a common endeavor; or will we become a divided nation?"); to Calvinist preachers; to Jesse Jackson, to Cicero and Aristotle.

And even the Clinton campaign won't deny outright that its candidate has ever used another politician's language. Asked about that in a conference call with reporters, Clinton communications director Howard Wolfson said, "Sen. Clinton is not running on the strength of her rhetoric." (Video of Clinton using a variation of Obama's signature "Fired up, ready to go" line has been circulated by the Obama campaign; it also appears at the bottom of this post.)

Moreover, Patrick and Obama share a campaign manager, David Axelrod, and the two claim that they had previously discussed elements of the speeches Patrick used and that Patrick had given Obama permission to use his words without citation. The two even share a slogan: Obama used "Yes, we can" in 2004, Patrick borrowed it in 2006, and Obama took it back in 2008. The New York Times' Jeff Zeleny reported Monday on an interview he conducted with Patrick:

In a telephone interview on Sunday, Mr. Patrick said that he and Mr. Obama first talked about the attacks from their respective rivals last summer, when Mrs. Clinton was raising questions about Mr. Obama's experience, and that they discussed them again last week.

Both men had anticipated that Mr. Obama's rhetorical strength would provide a point of criticism. Mr. Patrick said he told Mr. Obama that he should respond to the criticism, and he shared language from his campaign with Mr. Obama's speechwriters.

Mr. Patrick said he did not believe Mr. Obama should give him credit.

"Who knows who I am? The point is more important than whose argument it is," said Mr. Patrick, who telephoned The New York Times at the request of the Obama campaign. "It's a transcendent argument."

ABC News' Jake Tapper has called into question the chronology discussed by Patrick, though; on his blog, Tapper reports, "Obama was quoted using Patrick's language before the Summer of 2007 ... The claim that Patrick and Obama 'first' discussed this last Summer does not make sense." Tapper also provides other examples of similar language used by the two men.