There has been a bit of speculation on why Senator McCain chose Governor Palin as his VP selection. One popular suggestion seems to be that the Republican Powers That Be told McCain that he couldn't choose his buddy Senator Lieberman and dismissed his other selections as unworkable. Thus with a minimal vetting process we ended up with Palin for a VP selection... a choice that had an immediate goal of stealing Senator Obama's thunder while also galvanizing the neoconservative and religious bases. But there may be a more subtle reason for Palin's selection.
McCain is struggling for control of his party. Right now, the taskmasters behind the Shrub Administration are working hard to keep control of their base. It's a position that I witnessed in the Republican Party in Massachusetts where the Republican party faded into a non-entity while retaining control of the executive branch. The problem is, top-down power structures are unstable and once the base of charismatic Republican governors was used up, the entire party went belly up. McCain is smart enough to see this, but needs the support of the people backing the Shrub in order to gain the Presidency.
However, to choose any of the political players that Rove and crew want would risk diminishing McCain's own political star. He'd risk being overshadowed by his own VP selection. And what's more, he wouldn't have the selection he wants. Thus he needed to reveal to the Powers That Be that they don't have clothes.
Thus the selection of Palin. No doubt her name was bandied by Rove and crew as a potential candidate because of her beliefs and her ruthlessness. She is the perfect attack dog for the Republicans because the Democrats will treat her like stained glass. But she wasn't the first choice because of her fragility (in her own actions in the past and with what's happening in her family).
McCain jumped on this token candidate and ran with her. However, he doesn't expect Palin to make it to the end game. No doubt he realizes that Palin's negatives will come to light fairly quickly. After a week or two, Palin will end up bowing out, citing a need to consider her family and not having the time needed to be the Vice President. With her departure, Rove and crew will have egg on their faces because they suggested her to begin with. And McCain in the meantime will have benefited from contributions that rolled in in the wake of his selection of Palin.
At this point, he'll pull out his true choice. I suspect it will be Lieberman and he'll shove this choice down Rove's throat. The Republicans will have no choice but to accept McCain's choice for VP. Their own suggestion ended up a failure, and there's not enough time to force McCain to choose their own candidate. What's more, their investment in the presidency will be too great to bow out at this time. It's sink or swim for them, and they have to accept McCain's true choice for the Vice Presidency.
Further, the Democrats will be unprepared for a McCain/Lieberman campaign. Fresh donations will flow into the Republican campaign with Lieberman's own supporters (and part of the Jewish community) throwing their full support behind McCain/Lieberman, and the Democrats will be scrambling to find a means of coping with a new threat. The big danger for McCain lies with the disillusionment of many neocons who might say "heck with this" and not vote... resulting in an Obama victory despite the potential threat of a McCain/Lieberman last-minute campaign.