Who Runs the McCain Campaign? Or: Why Isn't Joe Lieberman on the GOP Ticket?

Stop me if you've heard this before: "They" didn't let John McCain pick Joe Lieberman as his running mate.

Former Bush strategist Matthew Dowd gives this claim the loudest voicing I've heard yet:

"They didn't let John McCain pick the person he wanted to pick as VP. When Sarah Palin got picked instead of Joe Lieberman... that whole ready versus not ready argument was not credible."

Today, most people are focusing in on the second part of Dowd's remarks -- "He knows, in his gut, that he put somebody unqualified on the ballot... and he put the country at risk, he knows that."

But I want to linger for a while on the first thought.

Who is the "they" that has veto power over John McCain?

Isn't this his campaign?

Isn't he running for the highest executive office in the land?

Isn't he aiming to be "the decider" part deux?

How is it possible that John McCain isn't even the decider in his own campaign?

Why isn't this the McCain/Lieberman '08 ticket?

This is a question worth getting an answer to.