Victor Davis Hanson is a classicist and historian at the Hoover Institution, Stanford University, and the author, most recently, of The End of Sparta, a novel about ancient freedom.

Recently, an open mike caught French president Nicolas Sarkozy and American president Barack Obama jointly trashing Israeli prime minister Benjamin Netanyahu. Sarkozy scoffed, “I cannot stand him. He’s a liar.”

Obama trumped that with, “You’re fed up with him, but I have to deal with him every day.”

Two days later, in one of the most bizarre op-eds published by the New York Times in recent memory, Paul Kane suggested that the United States could literally sell out its support for democratic Taiwan for about $1 trillion. He argued that the Chinese might be so thankful to us for letting them get their hands on the island that they might forgive much of what we owe them.

So why does the United States take risks in guaranteeing the security of countries such as Israel and Taiwan? Surely the smart money — and most of the world — bets on their richer enemies. The Arab Middle East has oil, hundreds of millions of people, and lots of dangerous radical-Islamic terrorists. China is more than one billion strong, with the fastest-growing economy in the world.

But President Obama should remember that America does not think solely in terms of national advantage. In fact, only the United States seems to have an affinity for protecting tiny, vulnerable nations. In two wars, and more than twelve years of no-fly zones in Iraq, America saved the Kurds from a genocidal Saddam Hussein...