And all of that assumes that none of the corruption associated with the Clinton Foundation comes out.
She is also insincere. She can't hide the fact that she's taken multiple stands on issues depending on what's most popular. She will have trouble justifying many of her current positions in a general election and fact checkers have already caught her in flips.
Then there is Hillary herself. She is not a warm person. Typically, she is most popular when she is away from the public spotlight. The more people see her the less they like her.
Hillary fatigue is another problem. She's been a public figure since 1992. I doubt if anyone under 30 can remember a time when she wasn't known. It's hard to generate Obama-level excitement for someone who has been around so long.
Her age is one of them. She will be as old as Regan when we was elected and his age did come up as an issue. Her health may also become an issue. There are rumors that she has health problems. All of the Republicans come across as young and vital compared to her.
All of that is generic.There are some specific reasons that Hillary won't be the next president.
There is also the leftward shift of the Democratic party. Obama ran as a blank slate then proved to be much further left than many of his supporters imagined. But the party has moved further left than Obama. This will be a defining election - has the country as a whole moved to the far left or just a portion of the Democratic Party? With all of the candidates running to the left of Obama, we won't know for sure until the general election but my guess is that the more centrist candidate will win. The Republicans have not moved anywhere near as far as the Democrats so they are more likely to nominate a centrist.
The wave elections of 2010 and 2012 imply that the country is reluctant to vote for Democrats unless Obama is at the top of the ticket and the country is suffering from Obama fatigue in general. Obama's executive orders have also cost him (and his successor) support.
There is little doubt that Hillary will win the nomination for presidency but there are a number of reasons that she cannot win the election.History is one big roadblock. In the last 100 years, a single party has only kept the White House for more than two terms twice. Reagan/Bush held it for 12 years and Roosevelt/Truman for an amazing 20 years, Roosevelt/Truman was a special case with Truman already in office when he ran on his own. Obama is no Reagan, leaving behind so much goodwill as to propel his successor into office in a virtual third term and Hillary is not running as Obama's successor.