A blogosphere spat is revealing an important fracture in the Democratic Party and liberal institutions.

The spat erupted nearly a week ago. The website Salon.com published a story reporting that Josh Block, a former spokesman for AIPAC, America's pro-Israel lobby, had collected a trove of provocative quotes from anti-Israel bloggers.

Here's Justin Elliott's breathless Salon lead:

The former spokesman for the American Israel Public Affairs Committee (AIPAC) is shopping a 3,000-word trove of opposition research against bloggers critical of Israel to friendly neoconservative journalists.

I've obtained an email sent by Josh Block to a private listserv called the Freedom Community, in which he throws around accusations of anti-Semitism against liberal bloggers and calls on other list members to "echo" and "amplify" his assault and "use the below [research] to attack the bad guys."

This is a referendum on whether it is more unacceptable in today's liberal Washington to use the language of anti-Semitism — or to protest the language of anti-Semitism.

You might wonder: Where's the story here? AIPAC exists to support Israel and refute attacks on Israel. In order to refute attacks, you have to keep a tally of those attacks. As for "throwing around" accusations of anti-Semitism — well, here's what Salon goes on to say. (Some of the references will be a little obscure, but we'll circle back and clarify as the story unfolds.)

He [Block] wasted no time throwing around more accusations of anti-Semitism.

"This kind of anti-Israel sentiment is so fringe it's support by CAP is outrageous, but at least it is out in the open now — as is their goal — clearly applauded by revolting allies like the pro-HAMAS and anti-Zionist/One State Solution advocate Ali Abunumiah and those who accuse pro-Israel Americans of having 'dual loyalties' or being 'Israel-Firsters' — to shape the minds of future generations of Democrats," Block writes. "These are the words of anti-Semites, not Democratic political players."

If charges of "dual loyalty" and "Israel first" do not count as anti-Semitic tropes, what does? To get ahead of our story a little, the nonpartisan Simon Wiesenthal Center made just this point in a statement released Tuesday:

The Middle East is a dangerous place — and not merely for people who live there. Unfortunately, it's becoming increasingly difficult in this country to take a position sympathetic to the Jewish state and in favor of the continuation of America's historic strong alliance with Israel without being called "an Israel Firster" and charged with "dual loyalties."... 

These odious charges have been around since Henry Ford in 1920 said "wars are the Jews' harvest," Charles Lindbergh in 1940 condemned Jews for conspiring to plunge America into World War II, and "Jewish neocons" were charged with colluding with Israel to cause the 2003 Iraq War.

Nonetheless, the reporting of Block's communication triggered anger and outrage among those whose words he quoted. Matt Duss, who heads the Middle East program at the Center for American Progress — the "CAP" mentioned by Block in his email — posted an angry riposte on Dec. 9, including these words:

As for Josh's outrageous anti-Semitism smear, I'm not going to bother responding, because I'm quite confident Josh knows that it isn't true.

Here are some samples of the comments to which Block took exception.

From Zaid Jilani, a blogger at CAP: 

"Israel Firsters fighting each other over whose position on the middle east conflict is more unreasonable."

"Waiting 4 hack pro-Dem blogger to use this: bit.ly/qT9eH2 2 sho Obama is still beloved by Israel-firsters and getting lots of their $$"

(CAP has since ruefully repudiated the use of the term "Israel Firster," and blogger Jilani has scrubbed his Twitter feed of the offending items, professing that he was "unaware" of the connotations of the term.)

From MJ Rosenberg, a blogger at Media Matters for America:

"Another good reason not to visit #Israel unless you are a rah-rah Likudnik."

"[The playwright] David Mamet did not become a conservative. He became an Israel First Likudnik. Conservatives are wrong as Americans."

"[Washington Post blogger] Jennifer Rubin thinks being accused by me of dual loyalty is an insult. Why. I say DUAL which is generous."

There are many more examples of this kind of talk. But the bite of the story is not that some bloggers offer obnoxious anti-Israel and anti-Jewish comments on the internet. Or that a former AIPAC communications director kept a tally of those obnoxious anti-Israel and anti-Jewish comments. Or that the bloggers reacted sharply to adverse comments on their obnoxious comments. It's a big ugly digital world out there, and a lot of harsh words are exchanged.

No, the bite of the story is what it tells us — not about some sharp-elbowed bloggers — but about the mainstream of liberal America. The Center for American Progress and Media Matters for America are two of the best-funded, most prominent, and most important liberal institutions in Washington, D.C. Block's digest (you can see his full collation here) raises the question: What are such groups doing trafficking in such stuff? Even more incredibly, when the story broke, it was not CAP and Media Matters that expressed remorse and offered corrective action. No, if The Washington Post is to be believed, the person in political trouble after the online spat is Josh Block — not the bloggers who trafficked in the "dual loyalty" tropes, but the person who protested the use of those "dual loyalty" tropes.

Here's Greg Sargent reporting in the online edition of The Washington Post:

Two top think tanks in Washington are mulling whether to sever ties with a controversial former AIPAC spokesman after it emerged that he was encouraging conservative writers to echo charges that critics of Israel are guilty of anti-Semitism, according to sources familiar with the discussions.

The fate of the former AIPAC spokesman, Josh Block, will be a big deal to people in left-leaning foreign policy circles in Washington. For them, the question of whether the think tanks will remain affiliated with Block will be seen as a referendum on the larger issue of whether demeaning Israel critics as anti-Semitic will be considered acceptable discourse among foreign policy experts.

The two think tanks in question are prominent centrist Democratic organizations: the Progressive Policy Institute and the Truman National Security Project. Block, a lifelong Democrat, has a part-time relationship with the two groups, although he now earns most of his living as a successful D.C. communications consultant.

Both PPI and the Truman Project adamantly refuse to comment on the Sargent story. But if the story is true, then Sargent's interpretation of it is exactly correct — if upside down.

As Sargent phrases it, the Josh Block story constitutes "a referendum on the larger issue of whether demeaning Israel critics as anti-Semitic will be considered acceptable discourse among foreign policy experts."

It would be more to the point to think of the Josh Block controversy this way: as a referendum on whether it is more unacceptable inside today's liberal Washington to use the language of anti-Semitism — or to protest the language of anti-Semitism.