1) The Republican convention bounce naturally expired.
The press's direct attack on Sarah Palin is working.After getting to read about Palin's record and see her for themselves, voters are starting to realize she's unqualified for the office and crazy to boot.
(3) The Wall Street collapse and the bailouts are turning voters toward Obama/Biden.
As you can see, I've taken the liberty of correcting one of the items.
Sarah Palin now has the lowest net composite favorability ratings of any of the four national candidates. She's at +7, compared to McCain's +9, Biden's +17, and Obama's +18. Palin is the rare politician who has so much wrong with her that she's actually managed to distract the press from focusing on the juicy but stupid stuff (can a woman with five kids be VP? What about her pregnant daughter?). Sure there's been some coverage on that, but (particularly given the media's propensity to focus obsessively on such things) they've been remarkably disciplined in sticking to problems of substantive merit.
And on these, most of her problems are strictly her own doing (well, her and the McCain campaign). Sure, there's probably nothing she could do forestall coverage about the fact that her own state is investigating her for abuses of power. And when the media discovered that sketchy hiring and firing decisions were a bit of a theme, that was going to come out too. But certainly she could have done better damage control. Sabotaging the state probe after promising to cooperate just looks bad. Having as your official excuse for why you fired the public safety commissioner that he was too aggressive in trying to bring down the rape rate? That's verging on parody territory. And many of the other issues are entirely self made. Palin wouldn't be getting kicked on this earmarks thing if she hadn't compulsively lied about her putative opposition to the bridge to nowhere. She could have diffused concerns about her foreign policy experience by showing knowledge and substance when interviewed by the national press. Instead she fumbled about and the McCain campaign was left trying to argue that having Russia in binocular distance was a sufficient foreign policy credential. Likewise on domestic policy -- if she demonstrated that she knew what she was talking about, she could easily have silenced a lot of critics. Instead, her analysis of the current Wall Street crisis left even conservative observers like Daniel Drezner begging for a translator. John McCain says she's America's resident expert on energy, but then she gives a figure for Alaska's proportionate energy production that's wildly off the mark (No, it's not 20%. No, it's still not 20% even if you restrict the metric to oil and gas). These are self-inflicted wounds.
Is the media in some way driving the public's recognition of these facts? Sure, obviously. But that's their job.