Why? Two reasons. Unlike Nixon, whose anti-Semitism seems to have been of a knee-jerk and atavistic variety, Bannon’s alt-right views — his opposition to free trade, a liberal immigration policy, “international bankers,” “corporatist global media” — are consonant with a sinister worldview that always finds a way to get back to a certain class of rootless cosmopolitans. His is not a personal bigotry so much as it is an ideological obsession. Its potential for destructiveness is that much greater.

The second reason is that political support for Israel is too important to tarnish through association with the likes of Bannon or European kindred spirits such as Holland’s Geert Wilders or Hungary’s Viktor Orban. Israel is not a latter-day Crusader kingdom holding out against a 21st-century Mahometan horde. It is a small democracy trying to uphold a set of liberal values against autocrats and religious fanatics sworn to its destruction. Zionists love Israel because of the way in which it brings together the values of individual freedom and Jewish civilization, not because of some blood and soil nationalism.

If Israel is going to retain mainstream political support, it cannot allow itself to become the pet cause of right-wing bigots and conspiracy theorists. That requires putting serious distance between Bannon and every pro-Israel organization, to say nothing of the Israeli government itself, by refusing to provide a platform for him and his ilk. Personal and national reputations alike always depend on the company one keeps. Not every would-be supporter deserves consideration as a friend.

That thought may have dawned on Sheldon Adelson, who skipped Sunday’s dinner and seems belatedly to have realized — too late for much comfort — how destructive Bannon and his brand of arsonist politics have become to the Republican Party and the causes it used to champion. The thought needs to dawn, too, on right-of-center Jews who have become so attuned to dangers from the woke-left that they have tuned out dangers from the alt-right.

Anti-Semitism is both the socialism of fools and the conservatism of creeps. If the past century holds a lesson for Jews, it’s to beware every form of illiberalism, including the illiberalism of those who purport to be on our side. Repair of the world may not be the central teaching of Judaism. But it’s always wise to stay far from those who wish to tear it asunder.