Unlike a normal non-profit, a church does not need to have a letter ruling in order to be a tax-exempt. If a church chose to blatantly break the rules and endorse a candidate, and the letter ruling was taken away (if the church had one), the church could re-gain their tax-exemption the next day automatically by not endorsing anyone. In order for a church to permanently lose it's tax-exempt status, it would have to endorse a candidate every single day, which is impossible to do, as Mr. Staver points out.
This browser does not support the video element.