Its the same problem Obama had to some extent. There is a subgroup of people in this country who I'll call "old people" who don't like what either Bill Clinton, then Obama then Hillary represent, which is a changing nation.
Bill Clinton ended the Reagan era far earlier than his acolytes expected. They bitterly resented that, hence the 9,000 investigations leading up to the absurd Impeachment hearings.
Barack Obama represents the end of the US being a uniformly white country in terms of power. If you're still nostalgic for the 1950's that must have been a kick in the teeth.
Hillary represents the rise of women. Always has, but its going to get worse now. Isn't there STILL a right wing organization dedicated to keeping women in the kitchen (whatever it is that Phyllis Shaffley runs)? If she wins, that's a kick in the balls. Really, the only thing left is an openly gay President.
People don't give up their way of life easily. That's why you constantly hear "we're losing our country" or "I don't recognize the country anymore". Its code for "white males are no longer running everything". When 99.9% of your party is made up of voters over the age of 60, the campaign Donald Trump is running makes a lot more sense.
Back to Hillary though, she and her husband are also magnets for an extremely lazy press corps looking for easy stories. If you're going to report on every absurd accusation over 25 years, eventually a greater portion of the public is just going to hear the word "investigation" over and over again and think there must be something to it, even if they couldn't tell you what.