If an entity's exemption is retroactively revoked, do its donors have to pay "Back-Taxes," too?

IRS won't come after good faith donors. It's just too much trouble for too little reward.

ie if a church preaches politics it will get its non profit status revoked

if the non profit violates any of the requirements that make it a non profit the status us revoked

ie no one an inure any benefit from the non profit, this does not mean some person cannot be an employee of the non profit

when the non profit has been declared to violate that status, the date of determination would be affective

when charitable donations were made over the years it was claimed to be a non profit the basis for those donations didn't change until the determination was made to revoke the non profit status

They could be!

When I donate to charity, I always ask for the 501(c)(3) EIN for my records. Cash donations of $250 must be confirmed by a letter. The letter should also include a statement to the effect, "No goods or services were received in exchange for this donation."

" Infernal Revenue Service (sic!) "

YOU don't use the term "sic" if you are the one doing the writing.

They could, but they won't be made to.