Why do candidates spend so much money?

The amount of money that all candidates spend on their elections is a tremendous amount!  It hasn't always been such a large of money though, back in 2004 during the presidential elections only about 1.9 billion dollars was spent.  Now a days that is about a third of what these politicians and every other high authority person spends on their elections.  Nearly six billion dollars has been spent on the midterm elections this year. Their is absolutely no need for that much money being spent, there are other ways to get your name out to the public without spending that much money.  It has obviously been done considering that there has never been that much money spent in past elections.