Once the current batter is done, the VP is the next up to the plate. One of the big knocks on Bush was by choosing Cheney he left the GOP win no on deck batter. Cheney age and health, plus his lack of interest in the job, meant we had no on deck leader once Bush was done.
Ryan is Romney's IOU to the conservative movement.
Now THAT is a great way to put it. Thanks. :)