If there were any real prospect of denying tax-exempt status to churches where the preacher strays into political territory, Catholic churches would be safer than most from censure.

That's because Roman Catholicism is unique among world religions it its degree of unity, as dictated by its authoritarian hierarchy. All that would be necessary would be for the Pope, or the National Council of Bishops, to declare that any directive to support particular candidates or parties is against Church policy, inferring that any individual priest who commits such an offense is a "renegade," not representative of the Church itself (and not important enough, or authoritative enough, to cause the Church as a whole to lose its preferential status).

On the other hand, many of the worst-offending preachers of political partisanship are independent pastors of their own "non-denominational" churches (or megachurches). They have no superior officers to cover for them the way a bishop, cardinal, or the Pope himself can claim higher authority than any individual Catholic priest.

These guys, who are basically CEOs of their own highly profitable business enterprises and personal feifdoms, could probably be denied their tax-exampt status much more easily than any pastor (no matter how politically oriented, inflammatory, offensive, or whatever) who is affiliated with one of the larger and more-tightly-organized denominations.