Exactly. Most presidents put a VP in place who becomes the de facto frontrunner when he retires. Bush didn't do that which left the GOP side in a free-for-all.
I've always suspected that McCain in 2008 was part of a deal struck by Bush and the party poo-bahs to get McCain on board for 2004, instead of running against Bush in the primaries again.
And if the 2008 campaign (and choosing Sarah in particular) made Bush think less of McCain, he has a short memory. McCain was undercutting Bush for eight years on everything from tax cuts to torture to Iraq. McCain was on the networks every night trashing Bush. That's why I refused to vote for him.
I think we have only elected two vice-presidents who served the president who selected him. Van Buren and Bush I.