As a millennial myself it is interesting there hasn't been more support from fellow millennials. With her opposition known to be a tax dodging, hateful, self obsessed, racist individual you would expect millennials to only go one way. But clearly some have gone the way of Trump, so overall I would conclude yes the national support from millennials is waning for Clinton.
Yes, millennial support for Hillary linton is waning nationally. Hillary Clinton didn't ever really have millennial support to begin with, especially after it was discovered that the DNC was conspiring to push Bernie Sanders out. It would not be a total surprise if the millennial demographic wrote Bernie Sanders in rather than vote for Hillary Clinton.
Millennials seem to be shifting away from Hillary Clinton due to her health issues and political positions that will most likely raise taxes on working millennials. Promising to provide free college education to all will cost everyone, including those people who have already paid their way through college and are now in the workforce.
Hillary continues to garner the support of people from all walks of life, while Donald Trump continues to lose his supporters. More and more people are seeing Trump for what he really is, and people are realizing that they don't want that kind of man to run this country. Hillary is getting some of those votes, while the rest will not be cast. Her supporters are certainly not switching sides.