I recommend the Wikipedia biography of John McCain. (use 'Wikipedia' and 'John McCain" as search terms). It seemed a fair and balanced treatment. He has lots to recommend him and lots to condemn him. He seems to me someone who is frequently an asshole, but sometimes commendably so, if that makes any sense. Well worth reading.
There is a saying that one should never get in bed with anyone crazier than you are. Probably one shouldn't elect as president anyone crazier than you are either.
Which raises the question of how many of your presidents would you say have been crazier than you are? I think we can all agree Nixon was a bit of a loon, with that lifetime fake persona. Ford may have been the sanest simply on the grounds of being dull and unimaginative. How about a brilliant gifted man with a compulsive self-destructive trouser snake problem? Are you saner than he? Or a reformed alcoholic who, according to the 12 Steps, has no more than a daily reprieve from his compulsive self-destructive impulses? Reagan strikes me as fairly sane in spite of being frequently self-deluded - like when he liberated Auschwitz though actually he was in Hollywood at the time. But his sunny optimism seems a healthy attitude.
If we regard McCain in this spectrum, with Nixon as the top scorer, of our presidents since Ike, he would be in the top half. He is definitely crazier than I am.
Another virtue McCain has is that, if he were elected, the president would still be someone older than I am. I have been able to dodge the bullet by a few months with both Bill Clinton and George Bush. Hillary Clinton and especially Barack Obama would both ruin my heretofore unbroken string of having been younger than every single president. Is it worth having some impulsive senile fool in charge of 'The Button' just to salve my feelings of getting old? Probably.
Imagine the US with an angry impulsive militaristic president while Russia is led by the angry impulsive militarist Putin. Hot times a-comin....?
Hillary is lookin' better all the time though I don't like her, believe her, nor trust her.