Thus, the idea of a limited government requires that society uphold and pursue the health of its most basic institutions. When a civil society is weak, government becomes strong. When the family breaks down, government grows stronger. When the essential institutions of society are no longer respected, government demands that respect for itself. That is a recipe for tyranny.

Much of this was essentially affirmed until the early decades of the 20th century when progressivists began promoting an agenda that fundamentally redefined the role of the federal government in public life. By the middle of the 20th century, the Democratic Party had essentially embraced this progressivist agenda, becoming committed to an increasingly powerful government--a government whose powers exceeded those enumerated in the Constitution. At the same time, the Democratic Party also began advocating for a basic redefinition of the morality that shaped the common culture. By and large, however, the Republican Party continued to maintain a commitment to the vision of America's founders, advocating for a traditional understanding of morality while also upholding the principle of limited government.

By the 1980s, the two parties represented two very different worldviews and two very different visions of American government. For decades, each party has acted rather predictably and in ways that accord with their fundamental principles. All of that, however, has now changed.

The 2016 presidential campaign has developed in an entirely unpredictable manner and, in many respects, represents a crisis in American democracy. This crisis is not limited to either party. Bernie Sanders, the Independent senator from Vermont, has won several stunning victories in the primary season over presumed Democratic nominee Hillary Clinton. While it is still extremely likely that Clinton will become the Democratic nominee, Sanders support among voters represents a populist flirtation with Democratic Socialism. This pattern is something few Democrats could have imagined just one year ago. What this foray into Democratic Socialism represents, then, is a radical adjustment of the Democratic Party's basic economic principles. Thus, even if Hillary Clinton becomes the nominee, the process will likely drag her even further to the left, eventually redefining the Democratic Party before our very eyes.

But if it is remarkable to see what is happening in the Democratic Party, it is absolutely shocking to see what is happening among Republicans. Traditionally, the Republican Party has established its reputation by standing for the principles advocated by the American Founders--limited government upheld by the health of society's primary institutions such as marriage, family, and community. Yet Donald Trump, the presumptive nominee for the Republican Party, represents virtually everything the Republican Party has typically defined itself over against. Clearly, both political parties are now redefining themselves. What is not clear is where each party will ultimately end up. What is also not clear is whether the American experiment can survive such radical political change.

As already noted, the American experiment in limited government requires that the citizenry and those who hold public office honor certain moral virtues and respect the institutions that are crucial for a society to rightly function. Yet, we now find ourselves in a situation where the three leading candidates for president show little to no respect for such institutions in their articulations of public policy.

This fundamental redefinition of the American political landscape requires Christians to think carefully about their political responsibility. Make no mistake; we cannot avoid that responsibility. Even refusing to vote is itself a vote because it privileges those who do vote and increases the value of each ballot. In truth, we bear a political responsibility that cannot be dismissed or delegated to others. Every Christian must be ready to responsibly steward his or her vote at the polls.

To put the matter bluntly, we are now confronted with the reality that, in November, Hillary Clinton will likely be the Democratic nominee and Donald Trump the Republican nominee. This poses a significant problem for many Christians who believe they cannot, in good conscience, vote for either candidate. As a result, Christians are going to need a lot of careful political reflection in order to steward their vote and their political responsibility in this election cycle.

Headlines from around the world tell us that other representative democracies are at a similar moment of redefinition. Political turmoil now marks the United Kingdom and also nations like France and other key American allies. Perhaps democracy itself is now facing a crucial hour of decision and a crucial season of testing. It is no exaggeration to say that democracy is being tested around the world; it is certainly being tested here at home. Yet if this is a moment of testing for democracy, it is also a crucial moment for Christian witness. This election cycle is going to be a particular test for American Christians--and we are about to find out if Christians are up to this challenge.

Albert Mohler is president of the Southern Baptist Theological Seminary in Louisville, KY.