The number of cases where an exemption has been lost is miniscule. One reason is that the IRS does not want to have the Johnson Amendment tested in the Supreme Court. Black churches endorse candidates all the time.

If Reverend Bob says "If you vote for A, you will go to hell", he is 100% protected by the First Amendment. Unlike our Commonwealth cousins, the government may not restrict such a religious judgment delivered in the course of exercising religious rights.

Fortunately for Catholics this rarely happens, and in fact I have been unable to substantiate one case of it occurring in the last election.