Congressional Hispanic Caucus chair Adriano Espaillat (D-N.Y.) is in what fellow House Democrats and other sources familiar with his race describe as an "existential" battle for reelection. Why it matters: The race embodies the Democratic civil war being waged across the country, with an establishment-aligned member of the party's old guard fending off a challenge from a younger leftist. Espaillat, a longtime fixture in Upper Manhattan politics, is touting support from New York Gov. Kathy Hochul and Attorney General Letitia James, as well as House Minority Leader Hakeem Jeffries (D-N.Y.). His rival, community organizer Darializa Avila Chevalier, is backed by the New York chapter of the Democratic Socialists of America, Justice Democrats and, most recently, New York City Mayor Zohran Mamdani. Driving the news: "I am so excited to be sitting here with Darializa and I am so excited to be endorsing her for Congress," Mamdani said in a joint MS NOW appearance with Avila Chevalier on Thursday evening.…