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Recently Mayor Bill de Blasio went to Iowa, not for the first time, presumably to vision-board a bid for the presidency despite his public equivocations. Over the course of two stops, one in Sioux City and another in Des Moines, roughly 65 people came out to see him, a number that might disappoint even organizers of a municipal town hall on new concepts in recycling. Never one to be deterred by absurdly long odds, he is on his way to Florida this weekend.

Let’s take it as a matter of certainty that with a 43 percent approval rating in the city he runs and no reality-television franchise to explode his fan base, Mr. de Blasio has little chance of becoming the next president of the United States. Delusion often protects us from acknowledging life’s unsettling ironies. Six years ago, when he was elected the mayor of New York, in a landslide of the kind not seen since 1985, he was poised to become the country’s most prominent voice of the progressive left.

It is easy to forget how concisely he delivered his message on the corrosive effects of inequality and how much it resonated when he campaigned in 2013, a moment when few politicians of his stature were branding themselves so definitively this way.

And yet by the time of the Democratic National Convention in 2016, Mr. de Blasio was relegated to a minor speaking slot scheduled during rush hour on the East Coast. This was partly retribution for his slow reflex to endorse the Democratic nominee, but it made clear how little currency he actually had with a new and growing movement he was so crucial in fomenting.