For me the most interesting part of all of this is difference in tone the news outlets take.

NY Times? A rift had always existed with the White House.
Facing a Rift, U.S. Spy Chief to Step Down – NYTimes.com

USA Today? A Senate report sealed his fate.
Intelligence chief resigns after scathing report – USATODAY.com

The AP and Reuters? He just resigned.
Spy chief Blair announces resignation | Reuters

Christian Science Monitor? He’s a scapegoat.
Intelligence director Dennis Blair takes fall for Christmas bomber – CSMonitor.com

CNN? He never had a chance.

Washington Post? Same theme but a slightly softer tone.
Blair’s resignation may reflect inherent conflicts in job of intelligence chief