Although Bush did not like Cheney's image as described by critics, accepting his resignation offer would help "demonstrate that I was in charge," he writes.
Bush said he talked to aides about asking Republican Sen. Bill Frist to run with him instead of Cheney, but ultimately stuck with Cheney because he valued his steady hand.
And Cheney told him he couldn't drop him from the ticket, we presume. But sure, George -- if your ghostwriter says you were "in charge," you were in charge. [ WP ]
More likely it was Rove who said no.