Princeton University is facing demands to fire a tenured professor once accused of being part of an Iranian campaign to murder the country’s enemies, The Post has learned. The school is also facing a congressional probe into why it hired the professor, Seyed Hossein Mousavian — who lectures on Middle East security and nuclear policy — despite him being a former top Iranian diplomat steeped in Tehran’s regime of fear. Mousavian was hired by the Ivy League school in 2009. Before that, he was a prominent figure in the Iranian government, both as a diplomat and editor of the Tehran...