Jansenism was a religious movement in Seventeenth-Century France that threatened Church and State. Its apologists, including Blaise Pascal and Jean Racine, thought their movement, based on its re-discovery of the teachings of St. Augustine, could save Christianity from the Protestants.
Its detractors thought Jansenism WAS Protestantism, but a Fifth Column of it, burrowing away within the Catholic Church. The two positions were irreconcilable.
The Jansenists lost, and lost catastrophically.
What an interesting lesson here in 'Church', and State.