Blogs such as The DailyKos, just like a broadcast station, newspaper, network or cable channel, are allowed to sell advertising AND promote various candidates for public office, according to a Federal Election Commission ruling. Opponents of such websites had argued that they should be treated as political committees. FEC disagreed, saying such sites clearly fall within the media exemption. In a March 2006 clarification, it said, "…that ‘costs incurred in covering or carrying a news story, commentary, or editorial by any broadcasting station…web site, newspaper, magazine, or other periodical publication, including any Internet or electronic publication,’ are not a contribution or expenditure unless the facility is owned by a political party, committee, or candidate."
RBR/TVBR observation: This is a key exemption, which extended to Howard Stern back when he was on radio, and it extends to Jay Leno, which is why he was able to play host to Fred Thompson last night.