All 4 of those races took place on decidedly blue turf, so Democrats winning them came as no surprise. In the case of Mamdani, it should also be added that he only got into this position because he ran against an extraordinarily flawed and weak field in which every single notworthy opponent was either disgraced or unpalatable to the voters. That being said, these elections once again show that the Dem coalition currently enjoys a strong advantage in low turnout off-year or special election environments.
Before Tuesday, I would have had Democrats as 55/45 favorites to win back control of the House in the 2026 midterms, now, I would put it at 60/40.