For the second time this week, Fox News Channel was driven to respond to criticism over on-air statements about Barack Obama, in this case for screen text that described the Democratic presidential candidate's wife as "Obama's baby mama." The term is often applied pejoratively to unwed mothers.

Television news organizations, facing unprecedented scrutiny, have often expressed contrition for poorly chosen words during this election season.

In a campaign that includes the first viable African-American presidential candidate, the lines of appropriate speech have become fuzzy. News organizations are under pressure from a broad network of self-appointed watchdogs, including organized groups like Media Matters and individuals. These watchdogs are likely to remain vigilant about gaffes, misstatements and potentially biased language through the November vote. Just this week, Gina McCauley, a well-known blogger in Austin, Texas, started michelleobamawatch.com to track the portrayal of Mrs. Obama in the news media.

In this campaign cycle, television news organizations have issued at least 10 apologies in total over on-air expressions. On Tuesday, a Fox News anchor, E.D. Hill, said she regretted suggesting that a celebratory hand gesture between Barack and Michelle Obama might be a "terrorist fist jab." On Monday, NBC News correspondent Andrea Mitchell apologized for calling southwest Virginia "redneck country."

Fox News is owned by News Corp. , which also owns Dow Jones & Co., publisher of The Wall Street Journal.