This does sound like extortion.
Turkey does have some legitimate claims though. Their economy suffered after the Gulf War, so they have to consider that when deciding how to be involved this time. Unfortunately, deciding that the original $20+ billion isn't enough and insisting on more seems wrong.
Former Senator Bob Dole made a good point on
Hardball the other night. Every day that goes by weakens the US position, by allowing some of the coalition of the willing to start digging for cash. Some monetary consideration is in order, but the phrase "the best friends money can buy" is becoming more true all the time.