Anyone who thought today's holiday might offer a brief lull in the campaign couldn't have been more wrong. This morning the Obama and Clinton campaigns held dueling conference calls over the issue of whether Obama "plagiarized" a 2006 speech from Massachusetts Governor Deval Patrick.

Here's the YouTube that's been zipping around the internet showing a side by side comparison:

Just how serious is this? Serious enough that the Obama campaign had Deval Patrick call Jeff Zeleny of the New York Times the following day to say he didn't believe Obama needed to credit him for the remarks:

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."

David Axelrod, the chief strategist for Mr. Obama who also advised Mr. Patrick, said Sunday that Mr. Obama adapted the words from Mr. Patrick. Mr. Axelrod said that he did not write the words for either candidate.

"They often riff off one another. They share a world view," Mr. Axelrod said. "Both of them are effective speakers whose words tend to get requoted and arguments tend to be embraced widely."

Meanwhile, the Clinton campaign is aggressively pushing the notion that irrespective of whether Deval Patrick gave his permission, Obama's failure to credit Patrick and to pass off the words as his own seriously undermines Obama's credibility. Responding to a question about Gov. Patrick's comments to the New York Times, Clinton Communications Director Howard Wolfson said:

"When an author plagiarizes from another author there is damage done to 2 different parties. One is to the person he plagiarized from. The other is to the reader, who has a set of assumptions and expectations that when you read words in a book they are the words of the author unless they are appropriately credited to another party.

So I think it's fine that Deval Patrick said that. But what I'm concerned about here is that the public has an expectation that Senator Obama's words are his own, unless he credits them to someone else. And so when you are running on your rhetoric and the power of your oratory and the words that you are using turnout to be someone else's, I think it undermines a very central and important premise of Senator Obama's candidacy."

The Clinton camp also sought to tie in recent criticisms that parts of Obama's economic plan, unveiled last week in Janesville, Wisconsin, looked remarkably similar to those proposed by Senator Clinton last year.

This story, now headlining the top of Drudge, is sure to rage on for days. On the conference call a British journalist raised the specter of 1988, when Joe Biden was forced from the Democratic primary after it became known he had lifted material from British politician Neil Kinnock without attribution. The current controversy won't end in Obama leaving the race, of course, but at the very least the episode puts Obama on the defensive in a contested race where he had certainly gained the upper hand in the last two weeks. Just how much damage it does remains to be seen.

UPDATE: Via Ben Smith, here's Obama's response at a press conference in Ohio today:

"He [Governor Patrick] has occasionally used lines of mine. I have occasionally used some words of his. I know Sen. Clinton has used words of mind as well. I don't think that is something that workers here are concerned about," he said, adding that "maybe I should have" given credit to Patrick.

Bottom line: "I really don't think this is too big of a deal," Obama said.