The nightmare vision focuses on a stark, painful moral choice.

It's Election Day. A Catholic voter who embraces her church's Catechism, or an evangelical committed to ancient doctrines on a spectrum of right-to-life issues, steps into a voting booth. This voter is concerned about the social impact of gambling, attempts at immigration reform, a culture fractured by divorce, battles over religious liberty and the future of the Supreme Court.

In this booth the choice is between Donald Trump and Hillary Clinton. Period.

"That's the scenario people I know are talking about and arguing about," said Stephen P. White of the Ethics and Public Policy Center in Washington, D.C., author of the book "Red, White, Blue and Catholic."

Many religious conservatives believe they "face a choice between two morally repugnant candidates," he added. "The reality of that choice is starting to drive some people into despair. … I understand that, but I think it would be wrong for people to think that they need to abandon politics simply because they are disgusted with this election."

This nightmare for religious conservatives is especially important since, in recent decades, successful Republican presidential candidates have depended on heavy turnouts among white evangelical Protestant voters and on winning, at the very least, a majority of "swing votes" among Catholics who frequently attend Mass.

While this year's election is in some ways unique, traditional Catholics and other moral conservatives need to realize that they are engaged in a debate that has been going on for centuries, said White. The big question: "Can Christians be good citizens?"

In an interview with the journal National Review, he explained: "The author of the second century 'Letter to Diognetus' addressed this question. Three centuries later, St. Augustine wrote City of God largely in response to the same question. … The question is about the nature and scope of the political good: Is the good of the political community compatible with Christian claims about the nature and destiny of the human person?"

At the moment, the choice is especially painful because religious believers are living, and voting, in an age in which up appears to be down and black appears to be white, said White, in a telephone interview. Suddenly it's controversial to argue that marriage is the union of a man and a woman, that children need mothers and fathers and that human beings are created, by God, as males and females.

So what about that voting-booth nightmare?

In one online essay, evangelical author Tony Reinke of the "Desiring God" website rounded up a list of 12 proposed voting options in 2016. There were, for example, five motivations for not voting -- including a conviction that voting is not a "Christian priority." Others may abstain to "send a message" of some kind.

Then again, he noted, religious conservatives could enthusiastically support a third-party candidate or quietly cast a write-in ballot for a symbolic figure of their choice. Among several "utilitarian options," religious conservatives could vote for the "lesser of two evils," perhaps hoping to negate one vote cast for the candidate they most oppose.

The final utilitarian options in his essay: choosing a major candidate based on faith that they would appoint good Supreme Court justices or that this candidate would "most likely avoid global warfare and the death of civilians."

Finally, Reinke quipped, voters can "pack up and flee before the wall is finished."

More than anything else, said White, distressed voters must realize that there is more to citizenship than voting in the White House race because "that invests in the office of the presidency a level of authority that simply isn't supposed to be there."

It's crucial for believers to pay attention to the "down ballot" national and state races that also affect American life, he said. Today, many voters need to be reminded of their responsibility to take part in practical issues at the local, community level.

Nevertheless, White said it is sobering to try to think about the current state of American politics "from the viewpoint of 30 years from now. … You look at the options we have right now and you have to wonder if our grandchildren will be asking us, 'Why didn't anyone have the courage to do something, to try to offer people some other choices?' "