"Years before the Purim story, Haman and Mordecai meet in the desert on their way to the capital. Haman lacked self-control, and ran out of provisions. Mordecai, being more level-headed, had rationed his food. Starving, Haman came to him begging for food. Initially Mordecai refused. (The guy was an enemy combatant, after all.) But later Mordecai made Haman an offer -- food in exchange for being sold into Mordecai's servitude.

But they had no parchment for a contract! Immediately Haman wrote on Mordecai's sandal: I Haman the Aggagite am the servant of Mordecai because I sold myself to him for a loaf of bread.

Mordecai didn't hold Haman to a contract signed under duress. But he did use it to humiliate his foe. When Haman later becomes Prime Minister (Esther 3:1-4) and demanded that everyone bow down to him, Mordecai showed him the sole of his sandal." (Medrash Esther vol V pg 60 in Buber's edition; Yalqut Shim'oni, #956)

What does all this have to do with Obama? Obama has no free will, he is an agent of Hashem. Why is he giving Israel a hard time? Because Hashem has sent him to do so - a punishment or a challenge for us. When Obama showed us his shoes he was saying: "Look folks, I am essentially your servant, because if you do good, Hashem will redirect me away from you; but if you do bad, Hashem will use me as a stick against you. I am your servant because my actions are totally dependant on your relationship with Hashem. Basically, all I do is up to you - as is written on this shoe!"