Editor's note: Howard Kurtz is the host of CNN's "Reliable Sources" and is Newsweek's Washington bureau chief. He is also a contributor to the website Daily Download.
(CNN) -- There are things that I admire about Rupert Murdoch. He has maintained a lifelong commitment to newspapers, long after it became clear that they were no longer profitable. He has a feistiness at 81, when he could be happily sitting on a yacht somewhere. He now spews his opinions on that newfangled social network called Twitter, and since he's the undisputed kingpin of News Corp., who's going to stop him?
But over the weekend, Murdoch sent out a tweet that went beyond outrageous to offensive, truly offensive. He played off the worst kind of historical libel against Jews. And while he later tweeted a semi-apology, it's not clear he understands the magnitude of his hurtful words.
The subject was the violence flaring in the Middle East, with Israel mounting airstrikes in Gaza after a long series of rocket attacks by the Hamas government. The message:
"Why is Jewish owned press so consistently anti-Israel in every crisis?"
That's right, he said Jewish-owned press, reviving the old canard about Jews controlling the media. Who, exactly, is he talking about?
Well, there's the Jewish heritage of the Sulzberger family, which owns The New York Times and Murdoch sees as a rival. Beyond that, most major media outlets are owned by public companies: Comcast (NBC), Viacom (CBS), Disney (ABC), Time Warner (CNN), Tribune (Chicago Tribune and Los Angeles Times), Gannett (USA Today). The Graham family, which owns The Washington Post, isn't Jewish.
And isn't there something rich in a complaint about media ownership by the man who controls Fox News, the Fox broadcast network, 20th Century Fox, the New York Post, The Wall Street Journal, The Times of London, the Sunday Times, Sky News, HarperCollins and other properties?
Beyond that, it's hard to take ethical lectures from a man who presided over a phone-hacking scandal in London that -- whatever his knowledge of it -- prompted him to close the longstanding News of the World tabloid and has led to the arrests of several of his former lieutenants.
What's more, Murdoch has never been shy about interfering in his newsrooms -- cozying up to politicians ranging from Ed Koch to Margaret Thatcher and Tony Blair -- so maybe he expects others to shape news coverage in the same way. Murdoch's Fox News portrayed Mitt Romney as a more viable candidate than he turned out to be.
But the heart of Murdoch's indictment is far more troubling.
He is suggesting that Jewish Americans have a hidden agenda in which their religion trumps their commitment to journalism. Since Murdoch finds these outlets allegedly dominated by Jews to be anti-Israel, perhaps he thinks they are of the self-loathing variety.
In a tweet on Sunday, Murdoch seemed to defend his use of the phrase: " 'Jewish owned press' have been sternly criticized, suggesting link to Jewish reporters. Don't see this, but apologise unreservedly." The wording is too cryptic to know for what exactly he's apologizing.
Earlier, Murdoch had tweeted that Israel's position was "precarious," adding "watch CNN and AP bias to the point of embarrassment."
Media mogul or not, he's entitled to criticize other coverage as he sees fit. But it's hard to evaluate his complaints since his 140 characters contain not a single example of questionable reporting.
The Middle East is a minefield for even the most scrupulous journalists. A photo of a wounded Palestinian often brings complaints that Israel is being treated unfairly and its casualties not highlighted. A story on Israelis wounded by Hamas rockets often causes grumbling that the Palestinian plight is being unfairly minimized. Murdoch is obviously strongly pro-Israel, which may mean he bristles at any coverage that doesn't sympathize with Benjamin Netanyahu's government.
One thing, however, is clear: Murdoch has undermined his own credibility by lashing out at what he calls Jewish-owned organizations. He should follow the advice that editors routinely give employees: Think hard before you tweet, for words, like weapons, can wound.
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The opinions expressed in this commentary are solely those of Howard Kurtz.