On one hand, their shared view is basically right: the advantage that Trump brings to table is that he will mobilize the so-called “missing white voters” that have not been turning out, and it is hardly clear that there will be enough of them.
But their numbers will be magnified by their concentrated presence in the battleground states: the Rust Belt, the Upper South, and parts of the Midwest. Relatively small increase in turnout suffices to tip quite a few large states in favor of the Republicans. This gives them a realistic chance of flipping the electoral map.
On the other side, will there be a comparable anti-Trump reaction among the Democrats? I don’t see where this will be coming from–least of all among the minority voters. In case of the African Americans, they already turned out in large numbers for President Obama in 2008, so it is not clear that they will be showing up to defeat Trump for Hillary Clinton in even larger numbers. Hispanics might or might not: the Hispanic electoral calculus is complicated. Among some subsets, especially those with little sympathy for immigration (Puerto Ricans being the obvious subset), there might be unexpected sympathy for Trump’s cause. These likely effects on their turnout and vote choice are further compounded by their distribution: too many minority voters are located in too obviously blue or red states. Increased turnout on their part will not significantly affect the electoral votes.
The other group who might be affected by Trump are educated voters, especially educated White voters. Here, the problem is that they already vote and are mostly set in their partisanship and ideology. So the question really is whether regular Republicans among them will be so disgusted by Trump that they would vote for a Democrat, especially if that Democrat should happen to be Hillary Clinton. This is the big question: the quote attributed to Ed Rendell in a recent NY Times article is that this will be the core of Clinton strategy in the general election. Existing survey results indicate that this is indeed a realistic scenario: Trump underperforms other Republicans by upwards of 10% among registered Republicans in hypothetical matchups against Sanders or Clinton: this is essentially the margin by which he falls behind other Republicans. Will enough regular Republicans actually bolt to Democrats because of Trump?
This is very hard to tell: there had never been a mass defection of educated, high propensity voters on this scale, as far as I know–people often talk of the role of Catholicism in the 1960 election, but I have never seen reliable numbers on those who defected for or against Catholicism beyond some apocryphal figures. Perhaps Trump is sufficiently disgusting a figure that he will cause such an upheaval, if he gets that far. But I would be hesitant to predict that many regular Republicans will openly defect like that.
The truth is that, unless the parties–both of them–engage with the so-called missing white voters, the danger of instability remains. Yet, this effort has been significantly missing. This article accurately describes the problem, but also observes that “any such confrontation (with the racism found in Trump campaign) must be paired with a full-court populist economic push. That’s what’s not happening. The Democratic Party long ago gave up on trying to engage or mobilize the white working class, and other than the early successes of his administration, even President Obama largely failed to secure the help he himself recognized was needed.” Therein lies the problem, if not in 2016, certainly in the long term.