The plagiarism accusations against Obama strike me as mighty weak. Here are the facts, as reported in the Washington Post's blog, The Trail:
Speaking in Milwaukee on Saturday night, Obama drew a standing ovation for a speech that included a defense of speechmaking — and his appeal to a sense of hope — as worthy leadership tools. He said, "The most important thing we can do right now is to reengage the American people in the process of governance and get them excited again....
"Don't tell me words don't matter. 'I have a dream.' Just words? 'We hold these truths to be self-evident, that all men are created equal.' Just words? 'We have nothing to fear but fear itself' — just words? Just speeches?"
During the 2006 campaign for governor, Patrick drew fire from his Republican opponent, who said his stylish speechmaking disguised a lack of substance. Among his responses was this one:
"'We hold these truths to be self-evident, that all men are created equal.' Just words? Just words? 'We have nothing to fear but fear itself.' Just words? 'Ask not what your country can do for you, ask what you can do for your country.' Just words? 'I have a dream' — just words?"
Here's why I don't excited by plagiarism allegations. As I've argued before, when a typical writer uses another's words, he commits two sins. (1) He deceives readers into wrongly giving him credit for originality. (2) He wrongly denies the original author credit that's important to the original author's reputation. That's why, for instance, scholars, whose stock in trade is original reasoning and writing, must be careful to properly attribute material they borrow from others, especially other scholars.
But I don't think this sensibly applies to politicians copying from other politicians. Politicians are admired for having sensible ideas and moving rhetoric. They're not expected to have ideas or words that are genuinely original in the sense of being their own invention; many high-level politicians' words are written by speechwriters, and even the ones that they write themselves are admired for their soundness or rhetorical effectiveness, not for their creativity. (Politicians are looked down on for having tired, boring, overused rhetoric or ideas that are the same as everyone else's; but not being cliché is not the same as being entirely original.)
Moreover, precisely because high-level politicians' words are usually written by speechwriters, there's little risk that close paraphrasing without attribution will wrongly deny anyone credit. Deval Patrick's speechwriter wouldn't get public credit for the words in any event; and Deval Patrick doesn't deserve public credit (except to the extent, which strikes me as too slight to make a difference, of deserving credit for sound editing, given that many politicians do edit their speechwriters' work).
It's possible that Patrick did write this speech or at least this passage, or that he's an extremely heavy editor of his speechwriters' work. But there's no reason to presume this harm to the original author as a general matter in copying politicians' speeches; and Patrick's defense of Obama is sufficient to make clear that in this particular case the author is either anonymous (if he's a speechwriter) or gives his consent (if he's Patrick).
Now it's probably marginally better to err on the side of giving too much credit rather than too little, just in case the original author would be annoyed (and is entitled to be annoyed), just in case some listeners expect your speeches to be original to you, and perhaps to indirectly reinforce a broader antiplagiarism norm that is sound in most other contexts even if it's inapplicable here. But when people fail to do this, especially in extemporaneous comments, they shouldn't be much faulted for it, and certainly not faulted using the label "plagiarism."
And, yes, I take much the same view as to Sen. Biden's using the words of British Labour Party leader Neil Kinnock in Biden's 1988 Presidential campaign.
UPDATE: James Taranto (Wall Street Journal's Best of the Web) has more.