"The Sea of Faith / Was once, too, at the full," Matthew Arnold wrote in "Dover Beach" (1867), "… But now I only hear / its melancholy, long, withdrawing roar / Retreating, to the breath / Of the night-wind, down the vast edges drear / And naked shingles of the world."

The roar Arnold had in mind was the sound of Christianity’s withdrawal from Western Europe. But his words describe equally well what is happening in the Greater Middle East. President Obama put it this way during his speech to the nation Tuesday evening: "For nearly seven decades, the United States has been the anchor of global security," including in this geographically central, resource-rich, and conflict-ridden region. But now we are weary of the burden. "A veteran put it more bluntly," the president said. "‘This nation is sick and tired of war.’"

America has left Iraq. America is leaving Afghanistan. America was so reluctant to participate in the NATO war that toppled Muammar Qaddafi in Libya, and so passive and hesitant in playing a role in Libyan reconstruction, development, and security, that our ambassador and three other Americans were killed in an assault on the U.S. diplomatic compound a year ago. The chief suspects in that attack remain at large. For over two years, America has watched confusedly as Egypt whipsaws between Mubarak, the Muslim Brotherhood, and General Sisi.

And for over two years America has done its best not to become involved in the Syrian Civil War. Even now, as President Obama says America must act in response to Bashar al-Assad’s latest use of chemical weapons, he also says there will be no boots on the ground, while his secretary of State describes any attack as "unbelievably small" and an unnamed official says that after a strike Assad "will still be able to eat Cheerios." To delay the use of American force, to forestall America’s reentry into the region, President Obama stunned the world in asking for a congressional authorization no one expects him to win, and by embracing a farcical Russian proposal to secure Syrian WMD that no one expects to work.

What happens when the sea recedes? The shoreline is exposed. Sand crabs and sea gulls and seaweed appear on the beach: Iranians and Saudis, Russians and Taliban. They come to fill the void left by the vacating American tide. The lower the tide becomes, the more daring the actions of the creatures liberated by its wake.

For several years now Americans have been comfortable in the delusion that the benefits, such as they are, of a global economy and of a world where war is a rarity can be enjoyed without cost. We can look inward, slash defense spending, gut the Navy, pull out from theaters of combat and from strategic bases, ignore the political character of Islamism, and otherwise pretend that at heart all human beings share the same feelings and want the same things, and life will go on as usual. And perhaps life will go on as usual, for most people, in most places in the country. After all: America is huge, protected by two oceans, and at peace with its neighbors.

But inevitably there will come a time when a lack of maintenance causes the international structure that America has built over decades to fall apart; when inwardness and self-preoccupation and "nation building here at home" exacts a cost of its own; when the flotsam and jetsam left behind by the receding tide, the sand crabs and seagulls and seaweed, begin to take over the shore. That time may have begun this week.

I do not say this as a supporter of President Obama’s proposed strike. I oppose it. Never has the president said what might come after his limited attack on Assad; never has the president provided a comprehensive approach to Syria or to the region that would secure American interests and limit the ability of radical Islam to acquire WMD; never has he seemed to have a clear sense of purpose and mission in Syria and beyond. Why grant war-making authority to a leader so feckless, a warrior so reluctant? Half-measures do not serve the American interest, and "proportional" force does not end conflicts. It prolongs them.

What I cannot stomach is the humiliation of my country on the world stage. Even the liberal Joe Klein admits that the presidential response to the Aug. 21 chemical attack in Damascus "has been one of the more stunning and inexplicable displays of presidential incompetence that I’ve ever witnessed." If Obama believed he already possessed constitutional power to strike Syria, he should have struck immediately, and have been ready to justify his actions. If he believed that the authority of Congress was required, he should have been willing to accept the verdict of Congress, which is clearly no.

But to adopt with such alacrity an improvised and cynical proposal by the Russians and Assad, and to spin that proposal as a victory, and as somehow his own, and to look paralyzed as the Russian autocrat uses the New York Times as a platform to spread conspiracy theories and lecture us on America, democracy, and international responsibility, is an embarrassment and an affront.

In the space of 24 hours President Obama went from being the enforcer of international norms to the enabler of Putin and the Assad regime. He has once again ducked responsibility for his words and actions, and in so doing has made the brutish leader of a defeated and broken empire the dominant player in Mideast affairs. And he has sent a signal: not to our enemies, who will continue to pursue their strategic objectives until they are met with force or deterred by overwhelming power, but to our allies, who must now realize that American foreign policy under Barack Obama is simply not serious.

The result will be more external involvement in Syria’s Civil War, rather than less, because the absence of American commitment and leadership makes room for further interference by Turkey, Saudi Arabia, the Gulf States, and Iran. And the result will be further proliferation, rather than less, because the absence of American involvement and the degradation of American control of the global commons of sea, air, and space encourages regional powers to arm themselves against Iran and North Korea and China. And the escalation of these regional arms races, the multiplication of regional conflict, the paralysis of international institutions, and the growing American disinterest in foreign affairs is a recipe not for peace but for war.

We may be able to ignore, and to avoid, those wars for a while. The history of our ambivalent superpower is one of vacillation between frenetic global activity and morose national introspection. But it would be simply ridiculous to believe we can enjoy living in the global village we built without paying for rent or for upkeep; or to believe, if you do not think the global village is any good, that the global gulag will be any better. And if you truly prefer a world shaped more by Vladimir Putin than by Barack Obama or George W. Bush, well, to hell with you. I give up.

It was another Victorian, John Stuart Mill, who observed in his essay on nonintervention (1859) that liberal apathy is an invitation to illiberal activity. "The doctrine of non-intervention, to be a legitimate principle of morality, must be accepted by all governments," he wrote. "The despots must consent to be bound by it as well as the free States. Unless they do, the profession of it by free countries comes but to this miserable issue, that the wrong side may help the wrong, but the right must not help the right."

Mill also predicted that

The first nation which, being powerful enough to make its voice effectual, has the spirit and courage to say that not a gun shall be fired in Europe by the soldiers of one Power against the revolted subjects of another, will be the idol of the friends of freedom throughout Europe. That declaration alone will ensure the almost immediate emancipation of every people which desires liberty sufficiently to be capable of maintaining it: and the nation which gives the world will soon find itself at the head of an alliance of free peoples, so strong as to defy the efforts of any number of confederated troops to bring it down.

Adrift and rudderless, the alliance of free peoples comes apart, the friends of freedom seek leadership and find none, and the wrong help the wrong to victimize the weak. Hear now the melancholy, long, withdrawing roar of American power, as we sink "down the vast edges drear / And naked shingles of the world."