Unlike Jason, I haven't reported on the internal workings of the McCain campaign. Nonetheless, I still think that another shakeup will happen. The announcement that Mike Murphy is not joining the campaign only means that Murphy will not be joining the campaign in the next few weeks. But McCain's campaign is far too unstable to keep the current dynamic in place for long. Imagine that it's early September, McCain is still behind in the polls and being pulled down by Bush, Murphy is still whispering in his ear that he's being thwarted by his Rovian staff, there's the promise of one final gonzo turn to Maverick-ism that appeals to McCain's self-conception... I still say it's a matter of when, not if.
Call it Murphy's Campaign Law. The internal instability of the dynamic between the candidate and his top advisors, multiplied by the candidate's deficit in the polls, produces an increasing frequency of internal shakeups as the time remaining until the election decreases.