On Monday, Dave Gilson produced this wonderful graph of spending by presidential candidates since 1860, in constant 2011 dollars. It suggested that we really have seen a departure in the last two cycles, with 2004 being the most expensive race up until that point, and 2008 burying 2004. Jonathan Bernstein points out that inflation-adjusted dollars really don't tell the whole story, since the country has been growing. So I've divided Gilson's cost figures by the number of votes cast* in each election (as recorded by David Leip), producing the graph below:
Like Jon, I don't see any particular problem with increased levels of campaign spending. Most of that spending consists of voluntary donations by wealthy Americans financing ads that inform middle-class Americans about presidential candidates. I fail to see the harm to the Republic.
*Jon suggests that it might be better to measure money spent per eligible voter, rather than per vote cast, since it is the eligible voters that the campaigns are trying to reach. I agree, but figuring out the eligible electorate in many of these years is a tad tricky. Millions of Americans were legally eligible to vote from the 1870s to the 1960s but nonetheless faced taunts, beatings, or death for trying to do so.
Update: See here to see campaign spending as a function of real GDP.