McCain was a shallow callow young to middle aged man, who dumped the "stand by me" first wife after she got older and heavy and handicapped, and hooked up with the hot blond young chicky with the big bucks and the daddy with connections.  Facing ultimate retirement on a military disabilty pension, McCain found the young blonde with all that beer money pretty irresistible.  McCain leapt from a being PTS-suffering heavy-drinking disabled veteran to a U.S. Senator (using his bio, her looks, and her daddy's money).

In Congress, McCain uniformly adherred to the Arizona paleo con line and got involved with dirty S & L money (during the last Bush-induced lending and property collapse).  After avoiding indictment for corruption, McCain covered his trail by espousing "campaign finance reform" and developing a reputation for independent rhetoric (always combined with party line votes).

During McCain's doomed quixotic presidential run in 2000, he preferred hanging on the bus with media (ever ready with a quipy sound bite) to actually campaigning among real people.  As a result, reporters fell in love and Republican voters rejected him.

So, once back in Congress, McCain flirted with switching parties (after Jeffords quit the Repubican caucus and control of the Senate was in the balance).  To induce him, our Congressional leaders, starting  with fearless leader Daschle, feel over themselves praising McCain's mavericky goodness.  

Then, in 2004, McCain was Kerry's first choice for vice president.  Repeat, McCain was Kerry's first choice for vice president.

So, if you're wondering why we can't touch McCain's obvious flaws, look to some of those now in campaign leadership positions, who spent the past 8 years innoculating McCain from criticism.  

Why can't we hurt McCain more?  Because OUR leaders reinforced McCain's bullshit "independent reformer" meme.