Just as Martin Luther said he preferred to be governed by a smart Turk than a stupid Christian, so should Americans prefer a faithless president able to maintain peace and prosperity than a faithful president liable to lead the nation to disaster. This doesn't mean that moral character isn't important. But the starting point for choosing a public official should be public competence. Moreover, Christian moral theology, at least, is not particularly helpful in constructing public policy. There is no scripturally mandated political agenda.
Some religious concerns are appropriately matters of government concern.
Abortion, for instance, involves another human life. If believers want the state to act, to stamp out drug use, for instance, they need to emphasize public arguments involving safety and crime. Moreover, these matters should not be treated as necessarily more important than other concerns. A growing economy, in which one can better care for one's family and the disadvantaged, is no small matter. Questions of war and peace, too, are significant.