TO cross the Atlantic to America, as I did recently from London, is to move from one moral universe to its opposite in relation to Israel’s war with Hamas in Gaza. Fury over Palestinian civilian casualties has risen to a fever pitch in Europe, moving beyond anti-Zionism into anti-Semitism (often a flimsy distinction). Attacks on Jews and synagogues are the work of a rabid fringe, but anger toward an Israel portrayed as indiscriminate in its brutality is widespread. For a growing number of Europeans, not having a negative opinion of Israel is tantamount to not having a conscience. The deaths of hundreds of children in any war, as one editorial in The Guardian put it, is “a special kind of obscenity.”

In the United States, by contrast, support for Israel remains strong (although less so among the young, who are most exposed to the warring hashtags of social media). That support is overwhelming in political circles. Palestinian suffering remains near taboo in Congress. It is not only among American Jews, better organized and more outspoken than their whispering European counterparts, that the story of a nation of immigrants escaping persecution and rising from nowhere in the Holy Land resonates. The Israeli saga — of courage and will — echoes in American mythology, far beyond religious identification, be it Jewish or evangelical Christian.

America tends toward a preference for unambiguous right and wrong — no European leader would pronounce the phrase “axis of evil” — and this third Gaza eruption in six years fits neatly enough into a Manichaean framework: A democratic Jewish state, hit by rockets, responds to Islamic terrorists. The obscenity, for most Americans, has a name. That name is Hamas.

James Lasdun, a Jewish author and poet who moved to the United States from England, has written that, “There is something uncannily adaptive about anti-Semitism: the way it can hide, unsuspected, in the most progressive minds.” Certainly, European anti-Semitism has adapted. It used to be mainly of the nationalist right. It now finds expression among large Muslim communities. But the war has also suggested how the virulent anti-Israel sentiment now evident among the bien-pensant European left can create a climate that makes violent hatred of Jews permissible once again.