...McCain's numbers (and the sample of editorials covering the numbers) started slipping definitively when Palin was turned loose for interviews, in tandem with the falling stock market, and the conservative press became just as critical in some spots as the liberal press.
You're lumping a number of factors into one cause-and-effect argument. Yes, the McCain campaign tried to micro-manage Palin right after the convention, and that made for bad interviews. The Gibbons and Couric interviews would have been difficult for any candidate, though, had the questions been exactly the same and the same type of "editing" applied.
No argument here that McCain's poll numbers started to fall when the stock market numbers did, but that reflects the public's fear and the tendency to blame the party in the White House for whatever happens, whether it be hurricanes, stock market crashes, or bad episodes of "Sex in the City."
There was also a fear amongst many conservatives (including me) that Palin wouldn't do well without scripting. Once she was freed from her handlers, though, that fear abated. Even the conservative critics mentioned--Will, Parker--have acknowledged as much.
Back to the original topic, though. Monegan disobeyed a direct policy from the Palin administration, and went to DC to lobby. That was more than sufficient justification for her to fire him. The trooper, Wooten, was definitely not fit to serve, and could have even been considered a threat to the governor's family. His supervisor said as much.
Enter French, a Democrat with no small partisan ax to grind, and Monegan, who was looking for revenge. He and Monegan teamed up to get the investigation going. It was payback time for Palin.
There was never any doubt as to what this "investigation" was going to reveal, because the findings had already been written before the investigation started. And French made damn sure that the investigation concluded before November 4th, even though even the most inexperienced political observer can see the questionable timing.
Is this a serious problem for McCain/Palin? My guess is that the Obama campaign has been doing some polling. If you see a lot of ads about it, then it's a problem. If not, then the Obama camp found that it's a non-issue for voters.