The men who fought in Vietnam, a war that symbolizes America's overreach and failures abroad, haven't ascended to the presidency in the way that the World War II generation did. But now, under President Obama, Vietnam veterans Chuck Hagel and John Kerry could get a chance to pull America back from its foreign entanglements.

Obama's nominations of these men, and the world's disenchantment with this president, signal that in his second term, the United States will have a less zealous mission in the world. The mantra isn't quite George McGovern's "come home, America," but we are not far from that Vietnam-era weariness of distant lands and causes. And who better than a president with a foreign pedigree and two combat veterans from the Vietnam War at the helm of the Pentagon and the State Department to give this retrenchment a sense of legitimacy?

All three men would disavow the charge that they are "declinists" who believe that American power is past its zenith, but there is an unmistakable pessimism at the heart of their worldview: We are flat broke, with pressing priorities at home. Foreign engagements begin well and end in futility. We don't know enough about the inner workings of these distant places to help more than harm. And besides, our embrace can suffocate those whose causes we might take up.

Syria burns, but we should hold steady and aloof, Obama's approach has made clear, because we have no way of divining the motivations of the rebellion - or the kind of society the rebels would build if and when the Assad regime falls. The law of unintended consequences haunts our deeds; we know well that American blood and treasure can be wasted at the altar of ideology.

The United States isn't that exceptional to begin with, this triumvirate believes. Hagel and Kerry have forthrightly said so on many occasions,while Obama has had to be more circumspect. In his first campaign for the presidency, he drew a distinction between good wars of necessity and bad wars of choice. But there is no mistaking the worldview of the politician who rose, unexpectedly, amid economic distress, to the height of political power.

The French have a fitting expression for the Obama phenomenon that broke out abroad, like a fever, in 2008: trompe l'oeil, a trick of the eye. Weary of the assertive nationalism of George W. Bush, Europeans and the Arab world welcomed Obama as a break with the "war on terror" and the American sense of embattled certitude. But the crowds in Paris and Berlin, not to mention Karachi and Cairo, mistook the animating passion of the candidate they had fallen for; they thought of him as a cosmopolitan man at home in the world. While he had lived in Jakarta as a boy, and had a Kenyan father and an Indonesian stepfather, he cut his teeth as a politician in the most American of cities: Chicago.

To the extent that the ideology of such a nimble man can be divined, the mission of his presidency has been the redistributive state at home. His legacy, as he sees it, will be his signature legislation, Obamacare. Yes, Osama bin Laden was killed on his watch, but the rescue of General Motors seems closer to his heart.

Two years or so into his presidency, the world caught on: Underneath the exotic name and the speeches referring to American follies abroad was a president who holds the foreign world at bay. The spell of his stirring speech in Cairo, in June 2009, has been broken. Instead of being taken in by Obama's magic, Muslims are burning him in effigy in Karachi. His approval rating among Pakistanis is as bleak as that of Bush.

Obama can live with the foreign world's disenchantment with him. He has a domestic agenda to focus on, and he has two combat veterans from the Vietnam War to scale back American commitments abroad.

"How many of us really know and understand Iraq, its country, history, people and role in the Arab world?" Hagel said on the Senate floor in 2002, in the debate that preceded and authorized the Iraq war. "The American people must be told of the long-term commitment, risk and cost of this undertaking. We should not be seduced by the expectations of dancing in the streets."

The Nebraskan was speaking of Iraq, but the war in Vietnam has haunted and defined him. He cast a vote authorizing the use of force for the new war, but it didn't take long before the former infantryman with two Purple Hearts gave voice to his disillusionment. As is well known, Hagel served alongside his younger brother, Tom, in Vietnam; both were wounded.

"We are each a product of our experiences, and my time in combat very much shaped my opinions about war," Hagel said in an interview with Vietnam Magazine last fall. "The night Tom and I were medevaced out of that village in April 1968, I told myself: If I ever get out of this and I'm ever in a position to influence policy, I will do everything I can to avoid needless, senseless war. I never forgot that vow I made to myself, and I tried to live by it during my time in the Senate."

By Hagel's moral code, his vote on Iraq was clearly a lapse in judgment. The passion with which he would speak about the war two or three years later, and his attack on the troop surge as a monumental error, felt like the penance of a man who believed he should have known better than to ever have supported the invasion.

If Hagel for years remained convinced that the Vietnam War was a noble cause badly executed, Kerry's path after his service as a Navy lieutenant was markedly different - as different, perhaps, as Nebraska and Massachusetts. His 1971 appearance before the Senate Foreign Relations Committee has trailed Kerry ever since. He spoke of American soldiers who had "raped, cut off ears, cut off heads . . . randomly shot at civilians, razed villages in fashion reminiscent of Genghis Khan."

It had been idle to launch that war, for there was "nothing in South Vietnam, nothing which could happen that realistically threatens the United States of America." The United States had gone there with lofty notions of freedom, but the South Vietnamese "only wanted to work in rice paddies without helicopters strafing them and bombs with napalm burning their villages and tearing their country apart."

There would be no taking back these words. In the eyes of Kerry's detractors, combat, three Purple Hearts and a Bronze Star would not fully acquit him. Emotionally tighter and more inhibited than Hagel, Kerry has put Vietnam at a good remove from his public persona. He has become a troubleshooter, traveling to foreign places but mostly to the chancelleries, to meet leaders and heads of state. Discretion is his code, since the attacks on him by Vietnam veterans during his presidential bid in 2004 rendered him a more cautious man. From his perch in the Senate, he has avoided controversies and redefined himself as an experienced mediator.

Kerry promises to be no more powerful at State than Hillary Rodham Clinton has been. This president, in the mold of Bush, is the "decider" on the crucial issues of our engagements abroad. Kerry won't challenge or resist the White House's primacy.

The world needn't worry about the assertiveness of U.S. power under Obama, Kerry and Hagel. It is people in distress - who might recall a different era when American armor and boots on the ground spelled the difference between rescue and calamity - who must come to terms with the near-certainty that the cavalry will not turn up.

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Fouad Ajami, a senior fellow at Stanford University's Hoover Institution, is the author of "The Syrian Rebellion" and "The Dream Palace of the Arabs: A Generation's Odyssey."