"The American people are weary. They don't want boots on the ground. I don't want boots on the ground. The worst thing the United States could do right now is put boots on the ground in Syria."

That was the leading Senate hawk favoring U.S. intervention in Syria's civil war. But by ruling out U.S. ground troops, John McCain was sending, perhaps unintentionally, another message: There is no vital U.S. interest in Syria's civil war worth shedding the blood of American soldiers and Marines.

Thus does America's premier hawk support the case made by think-tank scholars Owen Harries and Tom Switzer in their American Interest essay, "Leading from Behind: Third Time a Charm?"

There is in the U.S.A. today, they write, "a reluctance to commit American blood."

A legacy of Iraq and Afghanistan "is an unwillingness of the American public to take casualties on behalf of less than truly vital challenges. ... While such concerns may be admirable ... they are incompatible with a superpower posture and pretensions to global leadership."

You cannot be the "indispensable nation" if you reflexively recoil at putting "boots on the ground."

"If a nation is not prepared to take casualties, it should not engage in the kind of policies likely to cause them. If it is not prepared to take casualties, it should resign itself to not having the kind of respect from others that a more resolute nation could expect."

About the author's premise, that Americans are reluctant to take casualties, is there any doubt?

To demonstrate this, we need only address a few questions.

Would we be willing to send another army of 170,000 to stop a Sunni-Shia war that might tear Iraq apart? Would the American people support sending 100,000 troops, again, to fight to keep Afghanistan from the clutches of the Taliban?

To ask these questions is to answer them.

Should Kim Jong Un attack across the DMZ with his million-man army and seize Seoul, would Barack Obama's America, like Harry Truman's America, send a third of a million U.S. soldiers and Marines to drive the North out? Or would we confine our support to the South, under our security treaty, to air, sea and missile strikes—from above and afar?

Under NATO, the United States is required to assist militarily any member nation that is a victim of aggression.

If Moscow occupied Estonia or Latvia in a dispute over mistreatment of its Russian minorities, would we declare war or send U.S. troops to fight Russians in the Baltic?

Would we fight the Chinese to defend the Senkakus?

"America no longer has the will, wallet or influence to impose an active and ambitious global leadership across the world," Harries and Switzer contend. They cite Walter Lippmann, who wrote that a credible foreign policy "consists in bringing into balance, with a comfortable surplus of power in reserve, a nation's commitments and the nation's power.

"Without the compelling principle that the nation must maintain its objectives and its power in equilibrium, it purposes within its means and its means equal to its purposes, its commitments related to its resources and its resources adequate to its commitments, it is impossible to think at all about foreign affairs."

Though U.S. commitments are as great or greater than in 1991, the authors write, America is not so domineering as she was at the end of the Cold War, or when Bush 43 set out to "end tyranny in our world."

"The dollar is weak. The debt mountain is of Himalayan proportions. Budget and trade deficits are alarming. Infrastructure is aging. The AAA bond credit rating is lost. Economic growth is exceptionally sluggish for a nation that is four years out of a recession. And where 20 years ago U.S. military power was universally considered awesome in its scope, today, after more than a decade of its active deployment, the world is much more aware of its limitations and costs. It is decidedly less impressed."

Consider Syria, where the neocons and liberal interventionists are clamoring for U.S. military action, but "no boots on the ground."

Is there really any vital U.S. interest at risk in whether the 40-year-old Assad dictatorship stands or falls?

Turkish Prime Minister Recep Tayyip Erdogan, who has been calling for Assad's ouster for two years and transships weapons to the rebels, has now seen his country stung by a terrorist attack.

But though he has a 400,000-man NATO-equipped army, three times Syria's population, and a 550-mile border to attack across, Erdogan wants us, the "international community," to bring Assad down.

But why is Assad our problem—and not Erdogan's problem?

Harries and Switzer urge Obama to enunciate a new foreign policy that defines our true vital interests and brings U.S. war guarantees into balance with U.S. power—a policy where the first question U.S. leaders ask about a conflict or crisis abroad is not "how" but "why"?