It's funny that so many people think, and The Press continually hammers, "If you voted for Trump, you're a White Supremacist." Because Trump's core base is just that, alt-right wackos.
It may be funny but it is not what I am suggesting. Trump's base is made up of several identifiable components. The notable alt-right adherents are getting the "jumping off the Trump train" press today because they happen to be the ones who are jumping off and being vocal while doing so. Bit by bit, other components will leave as well. Some will stay no matter what but their numbers and political effect will be insufficient to serve as a political deterrent to impeachment.
Another faction is the anti-Hillary Democrats Ragman mentions above. They never considered themselves on board the Trump train but he received their votes on Election Day because they disliked Hillary more than they disliked Trump. Those soft votes became unavailable to Trump the day after they were cast.
While the narrative you describe may "quite inconveniently ... [ignore] all of those voters who voted for Obama and then voted for Trump." I do not. I referred to those voters a couple of posts above (the rust belt workers who may be wondering today why Trump has yet to keep his China-currency-manipulator pledge). They have yet to jump off the Trump train in a vocal way but they will as Trump disappoints.
Finding press articles about Trump losing his base is easy, because they all assume his base is the alt-right.
In this case, finding the articles is easy because the alt-right people are being very outspoken as they jump off the Trump train. As you correctly point out, they do not represent the entire Trump base, just a part of it. But it is a part Trump has now lost.
This completely ignores the fact that membership in the alt-right is miniscule. The narrative is that America is composed of two distinct groups: normal people (progressive liberals), and conservatives (racists one and all).
It may be THE narrative but it is not my narrative. The articles I cited document the departure of the alt-right people quoted in them and, presumably, others of a similar mindset. The articles speak of no one else and I have not suggested they do.
No one can throw a temper tantrum, or hold a grudge until they get their way, quite like a child. Or a liberal. So it's not surprising at all the the Trump protests are large and frequent, and mostly raw emotion. No intellectual arguments to be found, only name-calling vitriol.
Raw emotion sometimes coalesces into organized political action. The raw emotion expressed the day after Trump was inaugurated and at the many town hall meetings is so coalescing; not because of leadership from the Democratic party that is seemingly as lost in the headlights as ever, but because leadership is developing at the grass roots level. There is more to this than a temper tantrum.
This dynamic can be seen most clearly in Georgia's 6th Congressional District where a special election is underway. Republicans have held this seat forever but it may well be in play now. New on the scene are a number of grass-roots groups that have risen up to vote for the Democratic candidate. I do not know how they will fare but, because of this organized activism, the Democratic candidate will likely make an historically strong showing.
That is not to say the people rising up are Democrats. If not for the stringent ballot access rules of the two party system, a strong third party candidate may have emerged long ago. But with the rules as they are, the opposition is orienting itself around the Democratic ballot line. It is the easiest way for them to rally around and vote for an opposition candidate.
This race will be a fascinating one to watch. We'll get the chance to see not only how much the raw emotion has been converted into organized, effective activity; we'll also get to see how many Trump voters in 2017 will come through for a Republican now that Trump has been in office long enough for his voters to make a judgement.