Sometimes (though admittedly not often), Israeli even has the chance to achieve something at the United Nations. For example, just before the Trump administration announced its plan to withdraw, Unesco delayed a vote on an anti-Israel resolution. It might not sound like much, but Israel’s envoy to Unesco described it as an “achievement” that was “the result of three years of exhausting, frustrating and difficult diplomatic work.”

Enter President Trump. An Israeli strategy 70 years in the making is suddenly severely undermined. (According to news reports, the American decision was made without consulting the Israeli government.) Mr. Netanyahu then announced that when the United States quits Unesco, Israel will follow suit. It has no alternative. Israel can’t possibly let the United States leave an organization over anti-Israel bias and still remain a member itself. At the same time, Israel also can’t appear ungrateful toward the United States and hint that leaving Unesco might not be the best move for Israel.

But the truth is, Israel would prefer to continue its longtime strategy at the United Nations: staying a member and fighting for Israel’s interests. Israel would rather work on getting Unesco to improve — become a little less hostile, and even more so, less obsessed with Israel. But now that option seems to be in danger.

It’s possible that the election of the former French culture minister, a Jewish woman who has relatives in Israel, to lead Unesco might be a signal that the agency will improve. Or, perhaps, a recognition on the part of other Unesco members that the Trump administration won’t tolerate their anti-Israel shenanigans will sober up the organization.

But this can work only if Mr. Trump’s motivation for quitting Unesco is truly to curb its anti-Israel bias. If, on the other hand, his main motivation is to free the United States from paying for something he does not value, then he hasn’t helped Israel. He has hurt it by forcing it out against its will.