A great diary from Kos blogger, Shesk, put it this way: Palin is a play action pass.

Play Action Pass

Definition: A pass play where the quarterback fakes a handoff to a running back while he's dropping back to pass.
Examples: On a play-action pass, the quarterback hopes to fake the defenders into thinking the offense is going to run the ball. By doing so, he accomplish two things. He slows down the pass rush of the defense and he forces the defensive backs to make a decision between covering their assigned receiver or coming up to help stop the run.

….

To continue the analogy, the quarterback (the Republican Campaign) has faked us all into believing that Palin (the running back) has the ball, when it is McCain who is the intended pass receiver. The Republican offense is playing along, with right wing talk radio and Fox news acting as if Sarah Palin has the ball. The play is so well executed that even the game announcer (the media) thinks Palin has the ball. And, as the definition notes, this accomplishes two things: 1) It is slowing down the attacks on McCain, and 2) it is forcing us to make the decision between covering McCain or stopping Palin. And what are we doing? We're all going after Palin! Meanwhile, McCain is wide open, ready to receive the pass and charge into the endzone!

…

In the case of the election, everybody is playing as if Palin has the ball. PALIN DOES NOT HAVE THE BALL! THEY'RE THROWING TO MCCAIN! THEY'RE THROWING TO MCCAIN!

In election terms, this means, “Palin is not running for President!” McCain is Running for President! Look at McCain!”

1. Tell people that Palin's not running for President. Sure, everybody knows it, but they are acting otherwise. Hammer it and hammer it again: She is not the nominee. Quayle was not the nominee. Agnew was not the nominee. She does not matter. Stop looking at her. When someone mentions her, reply that she is not the nominee, McCain is.

1. Stop attacking Palin as a strategy: She doesn't have the ball; McCain does. Attack her in response to someone's mention of her, but quickly change the subject to the fact that she is not the nominee.

1. Ramp up our attacks on McCain.