He added that the letter was not about “left versus right wing,” but about the sex abuse scandal.

Nonetheless, Archbishop Viganò’s extraordinary 11-page letter, filled with personal attacks, has brought simmering ideological differences among American Catholics out into the open. Divisions in the church are quickly coming to a head, with many conservatives lining up to defend Archbishop Viganò and progressives rallying around Pope Francis, wrapping ideological competition and political maneuvering into what is quickly threatening to be the church’s biggest scandal in decades.

The stakes now are twofold: how the church will address sexual abuse and cover-ups among its ranks, and the power struggle emerging between conservative and progressive factions of the church’s United States leadership. The scandal around sexual abuse has escalated into the biggest test yet of Francis’ papacy, and the resolution will determine the future of the church in the United States.

Stateside, two bishops of small American dioceses, Bishop David A. Konderla of Tulsa, Okla., and Bishop Joseph E. Strickland of Tyler, Tex., stepped forward in support of Archbishop Viganò’s allegations against Pope Francis.

In an extraordinary move, Bishop Strickland issued his statement hours after Archbishop Viganò’s letter was made public, and instructed his priests to read his statement during Mass on Sunday.

“As your shepherd, I find them credible,” Bishop Strickland wrote of Archbishop Viganò’s allegations. Both bishops declined interviews.

Conservative American Catholics have been among the most vocal opponents of Francis’ agenda since he came into power in 2013. They have resisted his efforts to bring back into the fold those Catholics who have fallen away from the church because they are divorced and remarried, or are gay or lesbian, or are secular nonbelievers. They have also been opposed to Francis’ political priorities of protecting immigrants and refugees, questioning corporate capitalism and stemming climate change.