I've read the reason he waited so long is because Pickering will come up for a vote a year from now, and Bush is betting there will be fewer Democrats in the Senate so it will be easier to get him through.
EXACTLY. This is something of a 'one-time political fix', and something also of a 'now, or never' manuever. Just wish he had done it in the first 2 years though, so that we had a better shot winning Senate races in Louisiana and South Dakota, races we shoulda/coulda won if ALL the base turned out.