Hard to tell. The maximum for a single person is $2300 per election per candidate, with primaries and general elections counted separately. So the most a single person could donate to Obama (for example) would be $4600. However, campaign contributions can be bundled, so that $2000 Gates gave Bush in '03 could have been reported as $1000 from Bill and $1000 from Melinda. Most private contributors, though, only support a single candidate - these guys are supporting candidates in presidential, congressional, and state elections. All things considered, I think most of these donations are more philanthropical than devious - Gates and Allen are not trying to buy themselves congressmen. Rather, they are trying to guide the overall political direction of their homes, which is what rich people who no longer need the money are able to do.