Don't agree with either the premise or the answer you pose for it.
Dems are not 'hostage' to the Black Caucus. They enable the black caucus, they benefit from its frequently absurd antics and ability to stifle the opposition; but they're not hostage.
The dems are not hostage to gay rights, animal rights, abortion rights, or red wood liberation movements either; again, they encourage and benefit from them.
They benefit from all divisive social and political cults within the country...even those who, like your Congressional White Caucus, isolate themselves by villainising others.
Nonetheless, you are correct so far as you suggest removal of tax free status from any church that steps into the political ring; should happen as a default operation the instant someone steps up and says "vote for _________"
The Democrats have become no more than an amalgam of all the “scrap” material in our society......