If she runs, Harry Enten bets that Clinton will win the 2016 Democratic primary. He notes that she is polling at 61% already:
You might wonder how normal that is? It's in another stratosphere. I went into the Roper archives to examine races where no incumbent was running for re-election, and only Al Gore, at around 55% in early 1997 for the 2000 run, comes anywhere close. George HW Bush was only around 40% at this point in the 1988 cycle; Bob Dole was near 50% for 1996; and George W Bush was between 20% and 25% in 2000.
He goes on:
Some may be quick to dismiss early survey data, but almost always, those like Dole, Gore and now Clinton, who poll high this early and run, tend to march to the nomination.