Left-wing challengers to sitting Democratic mayors are shaking up at least four major races this year, tapping into exploding anger at the party’s establishment leaders.Why it matters: The races will offer early clues into the mood of progressive voters and the direction of the Democratic Party ahead of the midterms and the 2028 election.The big picture: Zohran Mamdani’s victory in New York City’s Democratic mayoral primary sparked a political earthquake after the 33-year-old democratic socialist ran a grassroots campaign focused on affordability in America’s largest city.His win garnered national coverage and highlighted the divisions within the Democratic Party over its direction on the war in Gaza…