Why is McCain still in Iowa?

Why is John McCain still campaigning and advertising here? Pollster shows him behind by over 10 points, he's never polled ahead of Obama here, and his stance against ethanol subsidies (which I personally agree with) certainly makes it an uphill battle. While this is a purple state that went narrowly for Gore in 2000, then narrowly for Bush in 2004, but this year, the independents I know are voting Obama, as are many moderate Republicans I know. So, again, why does McCain continue to spend time & money here? Perhaps if he starts to give up on the states in which he's polling so far behind, eventually it becomes mathematically impossible for him to hit 270 votes...

His interview with the Des Moines Register last week certainly didn't win him any friends while he was here either: