Who is trying to discredit the reporter who wrote about the ultra-conservative Koch brothers?

There have been at least three efforts so far:

• The Washington Examiner (which editorialized extensively against Mayer’s Koch brothers piece) did research trying to turn up evidence of Mayer’s political partisanship; they apparently didn’t find anything worth reporting.
• Elaine Lafferty wrote a pro-Koch response to Mayer’s story in The Daily Beast, complete with friendly quotes from David Koch—who was unwilling to speak with Mayer herself. TDB later added an editor’s note to the story admitting, among other things, that they "should have noted that the writer who interviewed Koch had been a consultant for the McCain/Palin campaign."
• And today, Keith Kelly reports on a third incident: The Daily Caller spent "several weeks" investigating a story that Mayer plagiarized work in her Koch brothers article, and in another story years ago. They found no evidence, and now they’ve dropped the story.