This is the letter I just wrote using the contact form on the White House website.
Dear President Obama:
During your campaign you promised to be a "fierce advocate" for gay rights. Since then, as many LGBTs and allies lost their patience with you, I stayed hopeful. I told myself that you can't be expected to fix every problem at once. I listened to people who said that, like Lincoln, you want to be forced to move forward on gay rights. I saw how few people were putting that kind of pressure on you, and told myself that you could hardly be expected to make a suicidal expenditure of political capital in its absence.
All that has changed. I've now joined the camp that has had it with you. You're planning to sit at the National Prayer Breakfast and pray alongside David Bahati? The thought is disgusting. If you do that, you will never reconcile your actions with your promise.
Please. Don't let history remember you as just another lying politician. And if your faith truly means anything to you, don't dirty it by sitting in the same room with an author of genocide.