Serious conversations about candidates and issues are essential to democratic citizenship in the United States. For me, this is the assumed starting point for any political discussion in our kind of democracy. I believe it was fundamental to the way our founders understood their new Constitution.
This means we place limits on the nature of such conversations. I suggest whatever argument you make it must be capable of rational critique based on evidence obtained from the natural world.
If you say that you know this to be true, because you believe it with all your heart and soul, it is a statement that does not belong in a democratic citizen to citizen conversation. I will believe you. I will respect you. You give me, however, no way to engage with you in a rational discussion between two citizens as part of their democratic citizenship.
Similarly, I think this is what Jefferson and others meant by the “separation of Church and State.” Discussions about State policy or choice of candidates cease being serious forms of democratic citizenship, when they veer into “it is God’s Will” territory. You say God has chosen so and so to be our next President. That is the end of a democratic exchange of views (with the aim of either finding my own views clarified or perhaps fallacious or your position seriously challenged and perhaps changed).
In such a democratic secular society we don’t lay down ultimatums about what our own God had to say or says about matters. Democracy obligates us to defend our own positions and open ourselves up for rebuttal in secular language. We give reasons for supporting one candidate or another, for embracing one policy choice over another. These arguments must involve facts and theories located in the natural not the supernatural world.
This is not true of Iran. In a society that requires belief in one particular interpretation of the Will of one Supreme Being, we should accept messages receive by the anointed from the One God. It would be an argument clincher, the end of the conversation. That is why they are not secular democracies.
If you and I seriously want to participate in our (the American) way of citizenship, we must develop our abilities to defend our positions in secular language—or retreat to the sidelines or work to overthrow our present system of government and establish a different form of democracy.
“it is God’s Will” is one of a special kind of phrase. It's called a thought terminating cliche. Ever since reading "Thought Reform and the Psychology of Totalism", I see thought termination everywhere. It makes it nearly impossible to hold a reasoned conversation. Not only does it cut off conversations but it keeps people from dealing with fallacies and cognitive dissonance in themselves.