What are the journalistic consequences of reporters donating to political campaigns?

[Commentary] One question which has gone largely unaddressed in the Keith Olbermann controversy is this: Is there a difference between donating to a candidate before they appear on your program and donating to a candidate after they appear on your program? What changes, if anything, with the exchange of cash?

Olbermann made his three donations following Democrat Raul Grijalva's appearance on his program on October 28, and following earlier appearances by his two other benefactors, Jack Conway of Kentucky and Gabrielle Giffords of Arizona -- he never interviewed or explicitly reported on the candidates post-donation. The Olbermann issue raises broader questions about the way that money can change reporting -- potentially overnight. What happens when a journalist reports on a candidate on Wednesday, donates to her campaign that night, then reports on her again on Thursday. What, if anything, has changed? How does that affect the journalism, and the way that journalism is perceived?