Insiders have long known that Giffords, Kirkpatrick and Mitchell are in trouble. This video shows that it's starting to become the conventional wisdom.
Vulnerability is self reinforcing--the more vulnerable a candidate looks, the more vulnerable he becomes. That's because vulnerable candidates draw top tier opponents and then they have trouble raising money as lobbyists start hedging their bets.
So, after Gabby impaled herself on Nancy Pelosi's health care bill (not to mention Cap and Trade and TARP), Jonathan Paton announced that he would resign his Senate seat in order to run against her. Paton looks credible enough that he managed to convince former Star and Capitol Times Reporter Daniel Scarpinato to come on board as his press guy. It's rare that someone leaves a real job in order to work for a challenger--that's why you see so many twenty something Political Science majors working for candidates. Scarpinato's decision--in addition to providing Paton's campaign with a high level of professional talent-- makes Paton look more credible as a candidate. That credibility make it easier for Paton to raise money and harder for Giffords to raise money.
After Ann Kirkpatrick's early missteps she was seen as vulnerable well before the health care debacle, that's why she's drawn a field that includes former Senate Majority leader Rusty Bowers.
To be sure, the incumbents will still raise the most money, but when an incumbent is widely seen as vulnerable, the money is harder to raise, the endorsements are harder to secure and the volunteers are harder to come by.
The opposite is true when a candidate is seen as unbeatble. No one who is credible will challenge him, so he becomes a sure thing. Democrats know that they can't beat John McCain in a general election so he's being challenged by Tucson City Councilman Rodney Glassman. I'm sure Glassman is a nice guy but he's destined to be a trivia question...just like the last Democrat who challenged McCain... can come up with the name?...30 seconds...ah, too bad. That would be Stu Starky who managed to get just over 20% against McCain in 2004.
Of course, I've predicted that McCain will draw a real Democrat as an opponent, but that's more of a face saving ploy for her than a legitimate shot at taking the seat.