This chart shows increases in the amount of campaign expenditures in American elections from 1971 to 2004. The X-axis represents each election period; the Y-axis indicates campaign expenditures in millions of dollars in House and Senate elections. Total campaign expenditures in both the House and Senate have increased steadily over this period. Because the entire House is up for election every two years, growth in House campaign spending has been larger and more consistent than spending in Senate elections. Only a third of the Senate is up for election every two years.