Klein notes that in those other cases, conservatives rallied to support their policy-deficient candidates on the theory that if liberals were attacking them, they needed defending. This time, that didn’t happen.
Whatever else the Republican abandonment of Akin represents, I don’t think it means that movement conservatives aren’t going to rally around “policy-deficient candidates” that come under attack in the future. The Republican backlash against Akin has the same cause as the episodes of rallying around unqualified candidates. The most important of these is the desire to support the party and/or the “cause.” National and Missouri Republicans evidently calculated that rallying around Akin would be too costly for the party’s prospects in the state and elsewhere, and they feared being dragged down with him, so they cut him loose at the first opportunity.
Defending Palin in 2008 was a partisan obligation for the movement conservatives that tried to cover for her lack of preparation, because the GOP was stuck with her once she was added to the ticket. Since it is possible for Akin to be replaced, and because his staying in the race will likely cost the GOP its chance of taking over the Senate and it may even be dragging down the presidential ticket, Akin quickly became expendable. Winning control of the Senate in 2010 was always a far-fetched idea, but this year it was a plausible goal for the GOP. Now it may slip out of reach. That is one of the main reasons why most of the GOP and the conservative movement came down on him as much as they did. It isn’t because they’re raising the standards they apply to their own candidates.