I just got back from a dermatologist for a check-up (growing up in Miami with outdoor summers requires this), and I asked her about McCain and skin cancer. He's had various types of the disease and I wanted to get a sense of whether he's really in danger or if this is one of those treatable forms of cancer. And she told me that basically, some skin cancers are not that bad, but malignant melanoma - the kind McCain has had in two separate places - is not one of those. It's bad. Real bad. And unlike most cancers, it doesn't really go away, even after years in remission. Sam Donaldson had it on his ankle, and thirteen years later it returned in the same spot. McCain has had it on two separate 'primaries' (not recurrences, which aren't as bad), and you can clearly see the post-surgical scars of having his lymph nodes checked (and partially removed). This is not a healthy guy, this is a 72 year old man with a fairly high likelihood of serious illness and death within the next few years.
I asked Senator Jon Kyl, a Republican, about John McCain's cancer, and he said that McCain is in remission. The video is above. You can see above that Kyl is taken aback, but he says that he trusts what John McCain told him. But why? That might be good enough for a Republican Senator, but why should that be the test for the voters? Why should we trust McCain on his medical past? It's not just that McCain has stretched the truth in this campaign, as even Karl Rove noted, or that he's acted as desperately as you'd expect a dying man to act when stretching for his lifelong dream of the Presidency, it's that McCain has simply refused to release his medical records to the public and confined select members of the press to a three hour window with no electronic equipment to examine his records. Brave New Films is on this question, and more than a thousand doctors have signed up to ask him to release his medical records. You should sign this petition and watch the video, it is downright scary. While this race is between Obama and McCain, President Palin is not an unlikely outcome (as Matt Damon noted).
There is precedent for covering up the health records of Presidents. JFK was a deeply unhealthy President, and the press covered up Reagan's increasingly obvious senility with phrases from Time Magazine like "If Reagan is afflicted by senility, some of the world's leaders might try a case of it." But this is different. McCain is contesting for the Presidency as a 72 year old man with a history of extremely severe malignant cancer, not just one case but several, as well as many other minor forms of cancer and various other diseases. He's on six different forms of medication.
I won't go into Palin, except to note that the question of her qualifications does matter in the context of McCain dying in office. Ultimately this is not a question of McCain's health, though, it's a question of his fitness for the Presidency; can you trust someone who won't release his medical records to run the country? Is he really going to place his own ambitions to become President above allowing the voters to know the answer to the very basic question of whether he'll be alive to serve them in the next few years?