Early in Moby-Dick, America's greatest work of fiction, Ishmael sits near the front window of a cozy inn, peering out into the stormy evening.  His eye rests on those fellow human beings passing by, unprotected from the cold and wet.  Ishmael is separated from this fate only by a fragile pane of glass, but it is upon that separation, Melville implies, that all of civilization rests.

This truth – the fundamental insecurity of existence and the fragility of those forces that protect man from destruction – is the basis of all conservative thought.  Conservatives recognize that existence is fraught with danger and uncertainty and that only deliberate effort joined with prudence and self-restraint can save mankind from the sort of debacles that have occurred throughout history, from the utter devastation of the Hundred Years' War to the Napoleonic Wars of the late eighteenth and early nineteenth centuries to the era of war and depression that reigned from 1914 to 1945.

The idea that such devastation has been consigned to the past is purely a liberal fantasy, intended to advance just the sort of agenda of state control that will actually initiate a new cycle of destruction.  Either liberals have not learned from the past or they willfully choose to ignore it.  Conservatives are wise because, like Melville's hero, peering out into the cruel night, they understand the dangers that always lurk.  It is a short step from peace and liberty to war and enslavement, and the only protection we have, to the extent that any exists, is eternal vigilance.

At present, we are faced with a progressive party that is not only oblivious to the danger, but pressing our nation in every possible way toward destruction.  Never in American history has there been such a concerted assault on our liberties.  Never has there been such hostility toward the sort of prudence that results in the amassing and bequeathing of wealth, one of the few means individuals possess of protecting their families against future suffering.  And with military funding near historic lows relative to GDP, rarely has there been such unconcern for our national defense (peaking at 41% of GDP during WWII, defense spending averaged 10% during the Cold War, declined to 3.5% in 2001, reached 5.7% in 2011, but is projected to decline to 3.8% in 2020).

The progressives, to employ Melville's metaphor, are determined to shatter the fragile barrier that separates us from danger.  They are determined to reduce America to the global standard of poverty and near total dependence on government that exists in hundreds of countries.  Not once during his time in office did President Obama condemn the antidemocratic actions of Hugo Chávez and Nicolás Maduro in Venezuela, presumably because he found nothing to condemn.  For the same reason, the left refuses to condemn the jailing of peaceful protestors in Communist Cuba, again because it sees nothing wrong with the tyranny of regimes that give lip service to a progressive worldview.

All that separates us from the rule of a Castro or Maduro is the protections afforded by our Constitution, yet Ruth Bader Ginsburg, supported by at least three colleagues, proudly declares her allegiance to a "living Constitution" that can mean whatever the Court wishes it to mean.  Each one of our constitutional liberties is a precious inheritance whose existence we owe to the wisdom of our Founders.  Yet many today, including some on the Court, seem to view the Founders as simply a contemptible group of paunchy old white men, many of them slaveholders.  Progressives assume that the Constitution, if relevant at all, is only a vague and entirely non-binding framework for contemporary actions.  According to this view, the Founders could not have known what specific issues we would face and how our society would evolve, and they were not particularly wise anyway.  If anything, they were hopelessly limited by the prejudices of their time and place.

That is the progressive view of all that protects us from the ruthless violence of extremism and despotism.  Given free rein, progressives would have our nation bankrupt, defeated, and morally degenerate within a generation.

Melville understood what is at stake.  In fact, he knew many of those individuals who helped found the progressive movement in America.  He witnessed the early nineteenth-century communalist experiments at Brook Farm, New Harmony, and Rugby, and he wrote of the dangers.

These radical experiments in egalitarianism and permissiveness failed in every instance, but their dangerous precedent left an impression on Melville and on his contemporary, Nathaniel Hawthorne, who lampooned Transcendentalist thought in his story "The Celestial Railroad."  The monomania of a tyrant such as Ahab, piloting the Pequod to destruction in an obsessive pursuit of the White Whale, seems an uncanny foreshadowing of today's progressive goals of radical environmentalism and social equality.

Ahab sacrificed his ship and all aboard, save Ishmael, in the service of his mad goal of destroying the creature he identified with evil.  Progressives today are equally obsessed with evil, a monomania that comes across in the fanatical attacks on liberty by left-wing leaders of the Democratic Party.  Elizabeth Warren's recent assault on attorney general nominee Jeff Sessions seems more than politics as usual: in its intemperance, it is typical of the left's conception of politics as a moral crusade.  This conception of politics disregards the most basic rules of civility, including the longstanding Senate prohibition against impugning the reputation of a fellow member of the Senate.

In nineteenth-century terms, progressives are what was called the Party of Hope, while conservatives are the Party of Necessity.  In time, probably sooner than we imagine, America will face a monumental crisis that will confirm the wisdom of the Party of Necessity and discredit the Party of Hope, though progressives will never acknowledge their failure.  Another global war, an economic collapse, a period of social malaise accompanied by civil unrest and violence – whatever form it takes, the crisis is inevitable.

The progressive response to this crisis will undoubtedly be something like "What difference, at this point, does it make?"  The conservative response is best summed up by Winston Churchill's "finest hour" speech (June 18, 1940) before the House of Commons, in which he addressed the fall of France to German forces and the miracle of the Dunkirk evacuation.

Churchill reminded his audience that, as a member of what Melville would have called the Party of Necessity, he had spent much of the last thirty years contemplating the defense of his country.  This defense rested upon the strength of both its army and navy, and, as Britain would come to see, upon its small but determined air force as well.  Most of all, Churchill urged the British people to acknowledge the reality of the danger they faced: "I do not at all underrate the severity of the ordeal which lies before us," he declared.

Facing the possibility of imminent invasion, Churchill reviewed the prudent steps his government has taken.  Summing up the situation, he stated: "I see great reason for intense vigilance and exertion, but none whatever for panic or despair."  Upon the defense of Britain depended "our Christian civilization" and "the continuity of our institutions and our Empire."  Rather than falling into the "new dark Age" of fascism, Churchill urged, "Let us therefore brace ourselves to our duties, and so bear ourselves that, if the British Empire and its Commonwealth last for a thousand years, men will still say, 'This was their finest hour.'"

Those words wonderfully express the spirit of conservatism.  It is one of vigilance, realism, prudence, and appreciation of established traditions and institutions.  It is a spirit that Melville would have understood and endorsed.  After all, Hitler was Ahab, and Ahab was Hitler.  And the madmen and madwomen who resemble Ahab are still with us.

A thin membrane, a resolute faith in our constitutional liberties and national identity, separates us from tyranny and destruction.  Those who would shatter that protective shield, the progressives, environmentalists, and socialists of the left, pose as great a danger to our future as fascism did to Britain in 1940, or as did Ahab, in Melville's imagination, to the crew of the Pequod a century before.  It is our duty and, as Churchill put it, our "glory" as conservatives to defend that tenuous barrier that protects us from the tyranny progressives would enact.  Let us remain safe and free, and let us do so by constant vigilance.

Jeffrey Folks is the author of many books and articles on American culture including Heartland of the Imagination (2011).