The majority of people will reject the Gospel (Mt. 7:14).
The majority of people rule in a democracy.
Therefore, a democracy will be ruled by those who reject the Gospel.
I realize there’s a fallacy there. The majority who get their way in a democracy will consist of different people at different times. On some issues, those who accept the Gospel may find themselves in the majority. But on issues in which the electorate are divided along religious and moral lines, those favoring traditional morality on the one hand, and those indifferent to it on the other, the devoutly religious are almost bound to find themselves outnumbered, and shouldn’t be surprised when it happens.
Some will reply that the majority of Americans identify themselves as Christians. Yes, but people self-identifying as Christians according to their own subjective lights, and accepting the Gospel as it exists objectively, are not necessarily the same thing. Hence, the wheat and the tares (Mt. 13:30).