Chancellor Friedrich Merz seems to have shot himself in the foot. Last week the leader of Germany — yes, that Germany — announced a suspension of weapons sales to Israel, if the arms are to be used in Gaza. What’s next, an invitation to Berlin for the heirs of Hitler’s World War II Palestinian Arab chum, Haj Amin al Husseini? Herr Merz hoped perhaps that this might calm Hamas supporters in Germany. If so, the politics might have boomeranged. 

Members of Mr. Merz’s own party, the Christian Democratic Union, say they were surprised by the announcement, on which they were not consulted. At this rate, they told the Süddeutsche Zeitung, Mr. Merz’s government “will be finished by Christmas.” Members of the CDU’s sister party, the Christian Social Union, are similarly up in arms, as are, well, arms manufacturers. Some 30 percent of Israel’s imported weapons are purchased from Germany.

Munitions-makers’ motives might go beyond fear of losing a client. A top German arms contractor, Renk, makes gearboxes for Israeli tanks. “From the German point of view, we have a responsibility to ensure that Israel is able to maintain its deterrence capabilities,” Renk’s chief, Alexander Sagel, told the Financial Times on Thursday. To maintain that, “plan B is that we relocate production of these specific transmissions to the U.S.,” Mr. Sagel says.

Such a move will undoubtedly delight President Trump, who welcomes the relocation to America of foreign firms. Mr. Trump also reminds us daily that America will sell, rather than donate, arms to European countries for use in Ukraine. Germany is one of Kyiv’s most enthusiastic supporters, as Berlin rightly says President Vladimir Putin started the war by invading a sovereign country. Why that logic doesn’t apply to Israel’s war is beyond us. 

The reason might be immigrants of Muslim descent, who march in European streets carrying images of suffering Gazans. The horrors of the October 7, 2023, invasion, which launched the war, are disappearing from Europe’s consciousness. In their minds, the good guy whose country was attacked, President Volodymyr Zelensky, deserves all the support in the world, while this morality play’s bad guy, Prime Minister Benjamin Netanyahu, must be shunned. 

By that logic, Mr. Merz’s move might earn him applause in some circles. Yet, it too might backfire, as two can play this game. “I think we have a relationship of mutual supply with Germany, and I don’t think they’ve forgotten that,” Mr. Netanyahu told Israel’s I24 television this week. Reminder: Last year Israel inked a $4.67 billion deal to supply Germany with the Arrow-3 missile defense system. It was Israel’s largest defense contract ever. 

The Arrow-3 will be part of Europe’s missile defense network, and help Ukraine defend against Russia’s endless assaults. Should Israel now retaliate by denying arms to Germany, as Mr. Netanyahu is hinting, Ukraine’s defenses might be weakened too. Political setbacks, German arms firms’ relocation to America, harm to Ukraine — all these could potentially force Mr. Merz to rethink his ill-conceived announcement denying weapons to Israel. 

The chancellor’s capitulation to angry street mobs of immigrants might shorten his career too: New polls show him now trailing behind the tough-on-immigration Alternative for Germany party. For decades Berlin was Israel’s most reliable European ally. Germans instinctively knew that their past demanded a strong bond with the Jewish state. Turning his back on Israel will leave an ugly stain on Mr. Merz’s legacy long after Germans forget his name.