What is the difference between political and interest groups?
We often think of politicians "buying" elections as something limited to a bygone era of corruption, but, in fact, it is still a central problem in the politics of the United States. Increasingly, federal law has attempted to make elections cleaner and more transparent by limiting the amount of money people can spend to support political candidates and to make sure that donors are clearly identifiable, so that, for example, when citizens see that George Bush and other Republicans received massive funding from big oil interests and then note that once in office those politicians then voted to weaken the regulations that prevent ordinary citizens from being harmed by bad safety practices leading to oil spills, voters could make the connection and vote sensibly against such politicians.
By allowing "interest" groups to be exempt from political spending rules if they only campaigned on issues rather than for specific candidates, the FEC intended to allow a balance between free speech and buying elections. So, for example, non-political interest groups could raise questions about the safety of oil pipelines independent of campaign expenditure rules because they were not specifically campaigning for a candidate only on an issue. The 2010 rulings allowing super-PACs was a major step backwards.