Kate Maltby is a broadcaster and columnist in the United Kingdom on issues of culture and politics, and a theater critic for The Guardian. She is also completing a doctorate in Renaissance literature. The views expressed in this commentary are her own. View more opinion articles on CNN.

(CNN) Subscribers to the London Times this Monday found a familiar face, Luciana Berger, writing about a wearily familiar topic in British politics: the resurgence of hard-left anti-Semitism. Berger is one of the UK Labour Party's highest profile Jewish MPs, a prominent activist since her college days. Three far-right trolls have served jail sentences for sending her racist harassment or death threats.

But what now worries Berger is the increasing online abuse she receives from social media accounts that claim to support the leader of her own political party, Jeremy Corbyn. With Corbyn in charge of the Labour Party, attention is shifting in Britain from the anti-Semitism of the hard-right to that of the hard-left. The eminent political scientist Vernon Bogdanor recently warned the Jewish community that "there can be no comparison between the minuscule anti-Semitic threat from the far right and the widespread legitimization of anti-Semitism by the Corbynite leadership of the Labour Party."

Not surprisingly, on Monday night Labour MPs passed a formal resolution calling on their own leadership to do more to tackle anti-Semitism. Yet this weekend, of all weekends, American Rep. Alexandria Ocasio-Cortez chose to publicly thank Corbyn for a mutually congratulatory phone call in which they discussed "the peace, prosperity, + justice that everyday people can create when we uplift one another across class, race, + identity both at home & abroad."

Clearly, Ocasio-Cortez did not ask how "uplifted" Jewish people in Britain feel by Corbyn. Since her tweet about Corbyn, Ocasio-Cortez has responded to Jewish community leaders' concerns by promising to "reach out" and reiterating her "deep fellowship and leadership with the Jewish community."

But it's not difficult for any American member of Congress to know that citing Corbyn as a political model might be bad idea. Were it possible to ignore his seeming tolerance for anti-Semitism, his post-truth attitude to political debate and his intrinsically anti-American foreign policy would still be reason enough to fear the contagion of Corbynism in US politics. But as it is, his tolerance for anti-Semitism is indeed impossible to ignore.

It is nearly a year since the British Jewish community congregated outside Parliament to protest the Labour leader's reluctance to confront anti-Semitism among his hard-left allies; nearly a year since Corbyn was found to have voiced support for an anti-Semitic mural depicting Jews as conspiratorial world manipulators, nine months since video of Corbyn emerged speaking alongside Holocaust deniers, suggesting that "Zionists" were insufficiently English to understand "English irony"; and six months since photographs were published of Corbyn at a memorial ceremony in a Tunisian cemetery for Palestinian leaders believed to have ordered the killings of Israeli athletes at the Munich Olympic games.

Corbyn denies allegations of anti-Semitism and that he tolerates anti-Semitism. Reporters who write about his contact with known anti-Semites are attacked by his allies as purveyors of " fake news ." (In the case of the Palestinian memorial ceremony, after a firefight of claim and counterclaim in the British media over the exact layout of the Tunisian cemetery, Corbyn eventually admitted to being "present" but not "involved" when a wreath was laid on the memorial to the masterminds of the Munich attack.)

Yet for someone who firmly denies tolerating anti-Semitism, Corbyn has a bad habit of attracting anti-Semitic company. No wonder Britain's three Jewish newspapers last year put their internal differences aside to call Corbyn "an existential threat to Jewish life" in Britain.

But let's put aside, if that's morally possible even as a thought experiment, the issue of anti-Semitism. There are other reasons for the Democratic Party to be wary of a Corbyn-Ocasio-Cortez alliance. Corbyn's left-populism is one model of one route the Democratic Party could go down as it seeks to build a movement powerful enough to cancel out the right-populism of President Donald Trump. They should beware it.

Corbyn, as he showed in the debacle over the Palestinian memorial, has the Trumpian gift of emerging from every credible new allegation against him as if he's proved demonstrably that he's the victim of a media smear campaign. Accused of offending Jews, he took offense . This approach may mobilize left-wing voters, but it leaves democracy poorer for it. Corbynism is a mode of politics that assumes bad faith as a starting point; it is not the way to counter the toxicity already unleashed into the public sphere by Trump.

Like Ocasio-Cortez, Corbyn carries extraordinary influence over millennial voters, tapping into the economic fragility of a generation for whom personal "capital" -- or the great British dream of owning your own home -- was something their parents could build but today's young people can't imagine. Like Ocasio-Cortez, he has been a critic of the way "the gig economy" erodes labor rights. And like his American counterpart, Corbyn's deepest political values stem from a fundamental skepticism of Western power and prosperity: what Ocasio-Cortez has recently called "this weird American dream mythology."

Yet like her, Corbyn and his supporters are known for spending more of their firepower on members of their own party than the enemy across the aisle. Corbyn had spent 30 years as a backbench MP without any seeming aspiration to hold party office -- a position that emboldened him to rebel against the party line, or "whip," 428 times during Labour's time in control of the legislative assembly.

The same leniency is not shown to MPs who rebel against Corbyn's leadership: Corbyn's allies have been making moves for some time to deselect MPs who break his whip from their constituencies. Since Corbyn's election as Labour leader, the phrase "F--- off and join the Tories" has become so common an insult, hurled online by Corbynites at Labour supporters deemed overly moderate or " centrist " that many moderate voters have decided to do just that.

Those told they're not welcome in Corbyn's party include the author and philanthropist J.K. Rowling , a major donor to past leaders. In 2010, Rowling wrote an op-ed urging her fans to vote for Labour's Gordon Brown, in a last-ditch effort to keep his failing Labour government in power. Accusing the Conservative "Tory" Party of treating single mothers like herself as "bogeymen," she wrote, "The 2010 election campaign, more than any other, has underscored the continuing gulf between Tory values and my own."

Nine years and a few public criticisms of Corbyn later, it is Rowling who is frequently attacked as a "raging Tory" by Labour members. Anyone who disagrees with the leader must be an enemy to the party as a whole, no matter how publicly they may have demonstrated their party loyalty in the past.

And yet the British electorate would still keep this government in power rather than vote for Corbyn. There could be no greater indictment of his candidacy.

Democrats are tempted by Ocasio-Cortez for all the reasons the Labour left first fell for Corbyn. She connects instinctively with young voters: If a journalist picks her up on a small matter like accuracy, she's able to rally her millions of social media followers to return fire on the press until many journalists would find the process of holding her to account simply exhausting. Corbyn's outriders at propaganda outlets like Novara Media and Skwawkbox specialize in doing the same. Corbynism offers the easy warmth of moral tribalism and of clearly distinguished enemies: Israel and anyone who's ever voted Conservative. The similar tendencies displayed by the social media tribes who rally around Ocasio-Cortez's every tweet should be a warning to the Democratic leadership.

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But that didn't stop Corbyn from hosting one of Maduro's top diplomats at the British Parliament just last week. Given Corbyn's lifelong criticism of US "imperialism," it seems that any dictator who criticizes the United States is a good dictator.

Ocasio-Cortez and her generation of New Democrats need to learn that you can't stand in solidarity with the international hard left -- and with Jewish Americans. But they could also take a look at Corbyn and learn that however much you hate the status quo, it's not good enough to simply position your politics as inherently oppositional. Life as a young upstart, or a long reputation as a rebel backbencher, is no qualification for government.

Destroy the establishment, sure. But have something planned to replace it. And try not to follow Corbyn's model.