Second there is the matter of historical and ideological associations. Le Pen aspired to be Gaullist, but her party retained a Petainist taint, a connection to fascism and a tendency to minimize its crimes, plus the inevitable far-right links to Putin and his nationalist international.

But Corbyn’s inner circle has a similar minimizing tendency where the crimes of Stalinism are concerned, plus the equally inevitable far-left affinity for Latin American authoritarianism. If the specter of long-ago Vichy lurked behind Le Penism, the specter of present-day Venezuela lurks not that far in the background of Corbynism.

Third there is the matter of terrorism and political violence. Le Pen, through her father and his allies, had an ancestral connection to the far-right violence of the Algerian war-era pieds noirs. But those paramilitary operations are rather more historically distant than Corbyn’s fellow-traveling with the Irish Republican Army at the height of its bombing campaigns, or his habit (for which he recently offered regrets) of offering comradeship to Hezbollah and Hamas.

In the wake of the recent Manchester horror and London attack, the Labour leader has been hitting May from the tough-on-terror right for not adequately funding the police. All’s fair in love and the last week of a campaign, but still it’s a little audacious, since Corbyn clearly has an old revolutionary’s soft spot for a certain kind of terrorist.

Now, one can concede all this and still cobble together a case that Le Pen would have been more dangerous to existing European institutions than Corbyn. She’s a French chauvinist; he’s a lefty internationalist. She wanted France out of the European Union; Britain has already taken that leap (and a Prime Minister Corbyn would probably make Brexit somewhat softer). She traded in clash-of-civilizations rhetoric about Islamic immigration; he’s fluent in the pieties of multiculturalism.

But some of this amounts to saying that it’s O.K. to elect an extremist with anti-Semitic and authoritarian and even terrorist connections if he or she just takes the official European Union line on immigration and monetary policy. Meanwhile Corbyn’s habits of mind on defense policy — think Chomsky with a dash of Trump — could threaten as much destabilization for NATO as Le Pen threatened for the Continent’s monetary union.

Again, I don’t think it would be a better world if Corbyn were being met with Le Pen-level fear and loathing. The entire populist phenomenon, left and right, is happening because our establishment is in need of serious unsettlement, and that can’t happen unless movements and ideas with extreme or disreputable associations are allowed into the conversation.