They can collect as much money as they want, and purchase advertising supporting or suppressing any candidate or political issue that they want. The last time I read the US Constitution, I was under the impression that I had broad protections regarding freedom of expression and association. Supposedly, I can speak in favor of issues that are important to me, and disseminate that information without governmental restriction. Supposedly, I can associate with people I like, for whatever reasons, including political. I completely oppose that.
People confuse equal opportunity with equal results.
In the US, any non-criminal can independently run for elected office. In case you are not aware, there are several US presidential candidates this year still in the running besides Bush and Gore. This is exactly what a politician needs to do in order to successfully pass legislation when they actually are elected to and become part of the government - be able to build consensus and persuade people to a cause. Why you Europeans would want to slant the system to favor politically-incompetent people to be elected to office is beyond me.