I wrote this a year ago. It may be more true now.
I recall G Gordon Liddy in 1995 or 96 speculating that if Bill Clinton got re-elected, he would move so far to the left that it would make your head spin. That sounded plausible to me at the time, but it didn't turn out that way. Clinton could not stop running for office. He had to keep his poll numbers up, not for any practical reason, but because that's who he was (is). His second term was spent casting about somewhat randomly for a legacy issue, putting out scandals, and not doing anything unpopular.
I forgot, and so did Liddy, that people don't suddenly develop strength of character that late in the day. Bill Clinton did not want to be president in order to accomplish something; he wanted to be president. We already see that in Senator Clinton's attempt to move to the center. It is not that she is too calculating that is the problem. It's that she is only calculating.
A Hillary Clinton presidency would go bad in the same way. Once elected, she would immediately do a few favorite things, then start on something bigger. While she would likely aim lower than nationalized health care, she would nonetheless pick something that would spend most of her political capital. But the specter of re-election would immediately begin to haunt her. She would want a second term more than she would want anything else.
After an initial leftward lurch, a Hillary presidency would be characterized by the same narcissism and drift as her husband's. I think that would be worse than an attempt at focussed liberalism.