Adriano Espaillat

Ten years ago, a little-known state lawmaker in Upper Manhattan staged a major upset, winning a congressional seat that had for years been central to Black political power and making history as the first Dominican American and undocumented immigrant elected to the House.

Now that history-maker, Representative Adriano Espaillat, is in a tough re-election fight of his own, resulting from the same type of shifting demographics that once propelled him to victory.

Mr. Espaillat, who has built the trappings of a small political machine and chairs the Congressional Hispanic Caucus, is facing a Democratic primary challenge from Darializa Avila Chevalier, an organizer and democratic socialist nearly 40 years his junior. And as Mr. Espaillat, 71, works to blunt the ascent of Ms. Avila Chevalier, 32, another prominent democratic socialist is seriously considering backing her.

Mayor Zohran Mamdani is strongly considering whether to endorse Ms. Avila Chevalier, according to four people familiar with the matter who were granted anonymity to share private discussions.

Mr. Mamdani had committed to supporting Mr. Espaillat last year, according to three other people familiar with the pledge. It came after the congressman dropped his support for former Gov. Andrew Cuomo’s mayoral bid, and got behind Mr. Mamdani after he won the Democratic primary.

But as the mayor has watched Ms. Avila Chevalier gaining momentum, he has reconsidered his decision.

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