Here we go again.

Four years ago, we were treated to countless news stories about the supposedly dramatic inroads that George W. Bush and the Republican Party were making among Jewish voters, long one of the most bankable constituencies in the Democratic coalition.

In the summer of 2004, MSNBC’s Tom Curry noted the “anxiety” of leading Democrats, who feared “that Bush, due to his removal of Saddam Hussein, his resolve in fighting Islamic terrorists, and his robust support for Israel’s government led by Ariel Sharon, is gaining ground among those Jewish voters who place their highest priority on Israel’s survival.”

Then the actual election was held, and Bush carried an estimated 22 percent of the Jewish vote—a gain of three points from his 2000 showing (entirely consistent with the growth of his overall support from ’00 to ’04).

Now, with Barack Obama positioned to win the fight for the Democratic nomination, we’re hearing the same doomsday prophecies again. Jewish voters, supposedly, will view Mr. Obama with alarm: He failed to “reject” instantly an unsolicited endorsement from Louis Farrakhan (after “repudiating” Farrakhan’s past statements); his church’s minister traveled to Libya with Mr. Farrakhan 24 years ago; and he once suggested that there might actually be some Palestinian people who are suffering. Oh, and don’t forget the Muslim rumors. And the picture.

Jewish voters, then, will then find comfort in the arms of John McCain, who enjoys the loud backing of Joe Lieberman and who will undoubtedly devote much time to reminding voters of all of the terrible things Iran’s Mahmoud Ahmadinejad has said about Israel—and how Mr. Obama has indicated a willingness to meet with the Iranian president. And just like that, Jewish voters will be in play at the presidential level.

“There is anxiety, there is concern,” a top New York Democratic activist told the New York Post’s Fredric Dicker this week.

Don’t count on it.

Only once in the modern era have Jewish voters wandered off the Democratic reservation in substantial numbers, when a majority of them sided against Jimmy Carter in his 1980 reelection effort. (Carter won 45 percent of the Jewish vote, to Ronald Reagan’s 39 percent and independent John Anderson’s 16 percent.)

Otherwise, Jews have been steadfastly loyal to the party, even when (as was the case in ’04) the Republican nominee had been certified as “pro-Israel” by influential Jewish leaders and groups. Even poor Walter Mondale racked up 66 percent of the Jewish vote while barely cracking 40 percent in the national popular vote in 1984.

This suggests that Jews, who make up about 2 percent of the electorate, will invariably give the benefit of the doubt to the Democratic nominee except in the most extraordinary and dramatic of circumstances.

Mr. Carter had become the subject of very exercised and very public condemnation from numerous Jewish leaders after he bluntly challenged Israel’s right to occupy the West Bank and was blamed (however unfairly) for letting Iran’s pro-Western government fall. Mr. Obama, by contrast, has done nothing to rile up such opposition. He has courted rank-and-file Jewish voters with calls to restore the Civil Rights-era ties between the black and Jewish communities and won countless endorsements from prominent Jews. And he has routinely prefaced remarks about Israel with an affirmation of the special relationship between the U.S. and Israel.

And the proof is in the pudding. The Clinton brand is a powerfully positive one for American Jews as a whole, and yet Mr. Obama actually beat Mrs. Clinton among Jewish voters in Massachusetts (52 to 48 percent) and Connecticut (by 23 points). And he ran practically even with her in California (48-44) and Arizona (51-44). He hasn’t fared this well in every state (He lost Jews by 20 points in Maryland, despite winning overall by 22 points), but the underground (and sometimes not-so-underground) fear-mongering has not prevented him from attracting substantial Jewish support.

In a general election, it is not implausible that Mr. McCain could eat slightly into the Democrats’ traditional share of the Jewish vote. Especially among older Jews, who are much more likely to vote on the basis of which candidate is more “pro-Israel” than the younger generation is, a McCain-led effort to portray Mr. Obama as soft on Iran could bear some fruit. Maybe instead of the 22 percent that Mr. Bush won four years ago, Mr. McCain will grab 28 percent of the Jewish vote.

But it takes an awful lot to prompt mass defections of Jews from the Democratic fold. And Mr. Obama has more than enough working in his favor to keep them there.