Barack Obama's decision to send 30,000 more troops to what he calls the "necessary war" in Afghanistan, while setting an 18-month deadline to begin withdrawing, seems set to define his presidency. If things go well, and a miracle takes place, Obama will be able to claim victory, withdraw the troops as promised and step smoothly into the 2011-12 election campaign in. Afghanistan could, however, turn into a nightmare that will destroy his chances of re-election.

The "surge" decision was made after a three-month review of the request from US commander in Afghanistan, General McChrystal, for 40,000 more troops. Obama's speech at West Point announcing the deployment was a difficult moment for him. He will have considered all options and carefully calculated the consequences of his decision, as well as the harsh reality he faces domestically and internationally.

If does not increase troop numbers, American and allied forces may not be able to reverse the forward momentum of the Taliban, which has been building since 2007. The Taliban might overthrow Karzai government, take power, and once again offer a safe-haven for al-Qaeda to plot terrorist attacks against America. But if he escalates the war in Afghanistan, he will have a hard time convincing his core supporters to accept paying for guns instead of butter.

Opinion polls indicate support for the war is falling and the public is losing patience. Obama's approval rating is plunging as unemployment soars past 10 percent. So he chose to send a complex and mixed message. On the one hand, he reassured the Afghan government, the Pakistan government and his NATO allies, that America will fight shoulder by shoulder with them until Taliban is destroyed or surrenders and security can be handed over to the Afghan army. He also asked NATO countries to make up the additional 10,000 troops requested by McChrystal. On the other hand, he placated the American public by setting a deadline for the start of troop withdrawal.

It is sometimes said, "The art of politics is to make the impossible possible." In the 20th century we saw some seemingly impossible things come about. Three cases spring to mind.

The first was the rapprochement between France and Germany. The two neighbors had been enemies for centuries but after the Second World War, they made a decision to work together more closely than anyone could possibly have imagined. Their new relationship was the basis of the European Union which now has 27 members and is beginning to look like a United States of Europe.

The second case was the fall of Berlin Wall and the peaceful reunion of West and East Germany. Since 1961, Berlin (and Germany) had been physically and artificially separated into two parts by the Berlin Wall which was built by East Germany under orders from the Soviet Union. But Mikhail Gorbachev allowed East Germany to let its residents to pass through the wall unpunished and shortly afterwards the wall fell.

The third case was the peaceful end of Apartheid in South Africa. As a student of international relations, I had never imagined such developments could take place peacefully. To me, these were all miracles.

Is Afghanistan going to turn out to be a miracle for Obama? He has three minimum objectives ---- to deny al Qaeda a safe haven; to reverse the Taliban's momentum and prevent it overthrowing the government; and to build the capacity of the Afghan security forces and government so that they can survive without foreign troops.