While all the speculation can be entertaining, I tend to think that since one of the notes came from a Secret Service agent, the one passed to W then Laura, then Jeb sees it and looks horrified, that it has to do with some sort of security threat. The President, the First Lady, several former Presidents and First Ladies, heads of state from around the world, all there in one place. Would be tempting for certain bad actors.
I've not seen that...
But I don't pay that much attention.