First, read the quotes of what John McCain said and compare to the title of this article. Note that nowhere in the quotes does John McCain say that Sarah Palin is or could be the next Reagan or Clinton. McCain is saying is that we have had Presidents who came from being state Governors and were underestimated by the media at the time because they were state Governors.
Second, note the pictures. Reagan and Clinton happy, and the obviously calculated nasty-looking Palin.