People like to vote for the face and voice they are most familiar with

–2012 election–
Fundraising over time:
http://www.opensecrets.org/pres12/weekly.php

PAC fronts:
http://www.opensecrets.org/pres12/indexp.php?src=hp

another money breakdown, though it’s missing data:
http://elections.nytimes.com/2012/campaign-finance

–2008 election–
http://www.opensecrets.org/pres08/index.php

–2004 election–
http://www.opensecrets.org/pres04/index.php?cycle=2004

The secret to winning an election? Money.