The feds are probing a shadowy nonprofit’s $100 million anti-Israel “war chest” allegedly amassed by a glamorous ally of Mayor Zohran Mamdani, a racecar-driving billionaire and a Texas private equity mogul, The Post has learned. The Department of Homeland Security is investigating a UK-based outfit known only as PFF, scrutinizing whether it illegally funneled donor funds to Al-Haq, a Palestinian group sanctioned by the US in September, sources said. Two sources with direct knowledge said federal agents are investigating more broadly whether the fund’s organizers employ opaque UK corporate entities to obscure cross-border financial flows. One insider said the “linchpin”...