Similarly, if you do not change your opinions as you mature as an individual, and as you receive more information about particular situations and the world in general, then you are 'an idiot and part of the problem in this country'.
Over the course of several years there have been countless new events and new revelations. Literally countless. Every single day every single voter has new experiences in life, gains new perspectives, and hears more of history than they knew before. It is impossible to know what precipitated any individual's change without asking that individual. In absence of that specific knowledge, it is not appropriate to criticize anyone changing their mind, particularly over such a large span of time.
Can a change in administration be the sole cause of such a change in heart? Perhaps, but it is uncharitable (to say the least) to dismiss changes in public sentiment as the product of partisan politics and simple minds. Uncharitable, and unproductive.
If the overwhelming pattern is that the members of a single party change their views on multiple issues in concert, particularly of those shifts involve disavowal of prior views (or even diametric opposition to views previously held), while those of other parties (not just the primary opposing one), or persons outside that political system (e.g., in other countries) don't, and there's an expressed policy of opposing a party or its head, then I think the suspicion that the shift is largely partisan is rather well founded.
