May is Jewish American Heritage Month, and President Biden is in a pickle. Call it a kosher dill.

Mr. Biden has acknowledged that “antisemitic incidents are at a record high.” Describing physical assaults on Jewish Americans and harassment of Jewish students, Mr. Biden observed, “It’s unconscionable. It’s almost unbelievable. It’s despicable.” He calls antisemitism today “a stain on the soul of America.”

Mr. Biden is describing America during his own administration. He is describing crimes committed under his watch. The question is: What will he do about it? 

During Tuesday’s White House celebration of Jewish American Heritage Month, Mr. Biden promised his Jewish supporters that he would deliver a “national strategy to counter antisemitism” that would be “the most ambitious, comprehensive effort in our history to combat antisemitism in America.”

This sounds grand. But there’s a fly in the ointment. We know that there’s a problem, because if Mr. Biden’s policy team were working smoothly, he would have announced the plan during Tuesday’s White House ceremony. 

Symbolically and politically, that would have been the right move, unless Biden were struggling. And we know why he is struggling. The problem is his base. The political fault-line in the Democratic Party runs right down the middle of the Biden antisemitism plan. 

Mr. Biden is on strong political ground when it comes to right-wing antisemitism. He has been good about condemning neo-Nazis. At a Howard University commencement address on Saturday, Mr. Biden called white supremacy “the most dangerous terrorist threat” to the American homeland. His base will always applaud Mr. Biden when he condemns prejudice on the right. 

They are not so united when it comes to antisemitism on the left. Just last week, as hundreds of rockets were fired at Israel by Palestinian Islamic Jihad, Representative Rashida Tlaib hosted, with support from Senator Sanders, a “Nakba Day” event that condemns the establishment of the State of Israel as a “catastrophe.” 

At the same time, Ms. Tlaib introduced a resolution for the United States to formally recognize that the establishment of the Jewish State was such a catastrophe. It is inconceivable that members of Congress would treat any other nation or people in this way — especially one under violent attack by a designated terrorist organization. And yet Ms. Tlaib’s actions reflect the perspective of a significant part of the Democratic base.

Mr. Biden’s challenge is to address left-wing antisemitism when extreme anti-Zionism is now espoused by left-wing congressional Democrats. Mr. Biden cannot issue a national plan that merely weaponizes antisemitism charges against Democrats’ political adversaries. 

It is now too obvious that this bigotry has grown at both extremes of political opinion. If Mr. Biden fails to address bias on both sides, it will become obvious that he is exploiting anti-Jewish hatred for political purposes. He needs to address antisemitism across the board. And that’s where the politics get hairy.

Although Mr. Biden’s plan will include more than 200 policy plans and proposals, there is one that matters most: definitions. His mainstream Jewish supporters, who reside on the center-left, want a strong national plan. This can mean a lot of things, but it means one thing most of all. 

The organized Jewish community want the plan to be based on the International Holocaust Remembrance Alliance’s Working Definition of antisemitism, which is the only definition that encapsulates antisemitism from the right and the left, including when criticism of Israel crosses the line into antisemitism. 

That is why this is the definition of antisemitism embraced as the gold standard by most American states, dozens of nations, and is the cornerstone of the EU’s landmark strategy for addressing antisemitism.  

Most importantly, the organized Jewish community has also made clear they want the plan to avoid any reference — not even a footnote — to the diluted alternatives, such as the left-wing Jerusalem and Nexus definitions. On Wednesday, the Anti-Defamation League’s Jonathan Greenblatt, for example, admonished that “no other definitions work.”

At the same time, Mr. Biden’s hard-left supporters despise this internationally agreed-upon definition. They prefer it be omitted because it exposes the discriminatory basis for the demonization and delegitimization of Israel. 

Such disclosures infuriate anti-Zionist activists, because their own attacks on Israel are tinged with bias. As a fall back, if Mr. Biden’s plan is based on this definition, these activists would like the plan to elevate other definitions as well. 

To legitimize the definitions meant to mask antisemitism from the left, however, would be viewed as a betrayal of the Jewish community, including Mr. Biden’s center-left supporters, and undermine his entire plan.

The resolution to this drama is coming fast. On Wednesday,  the State Department’s special envoy to monitor and combat antisemitism, Ambassador Deborah Lipstadt, told Jewish Insider that the Biden plan could be released “in the next few days” or “next week.” That could be good news. Or it could be very bad.

The best-case scenario is that Mr. Biden’s plan is as strong as the European Commission’s antisemitism strategy, which uses the international working definition. The next-best alternative is that it contains no definition of antisemitism whatsoever. This would be seen as weak and cowardly, but at least it would not undermine efforts to address antisemitism elsewhere. 

The worst-case scenario would be for the plan to mention one of the more controversial alternative standards supported by the far left, undermining international efforts to coalesce behind a single standard. That result, to be sure, would be the real catastrophe.