Mayor de Blasio is in Iowa campaigning for president.

The mayor announced yesterday that he would seek the Democratic nomination in a three-minute video titled “Working People First,” in which he emphasized his accomplishments in New York City, calling his hometown “notoriously tough” and the place where he “beat” President Trump .

At its most basic, Mr. de Blasio is selling the idea of New York City to a national audience. The city’s big, it’s diverse. Crime’s down and the economy’s up. If voters like the New York story, Mr. de Blasio believes that will benefit him when votes start getting cast in 262 days.

[Mr. de Blasio became the 23rd Democrat to join the race, doing so against the counsel of his advisers.]

Let the examination of Mr. de Blasio begin!

The city is diverse but not integrated; just look at its schools. Public housing is in crisis, and the federal government has stepped in. The police’s use of force has been scaled back but has not been entirely transformed.

Polls have shown that many city voters oppose Mr. de Blasio’s candidacy , and nationally he must overcome formidable deficits in polls and fund-raising. Yesterday, protesters outside ABC’s television studios in Times Square (where Mr. de Blasio was on “Good Morning America”) were chanting, “Can’t run the city, can’t run the country.”