Immigration. While the GOP has been the party of immigration restriction since the 19th century, the rhetoric is clearly different. Take the issue of Islamic immigration. During the 2000s much of the opposition to Islamic immigration came from "America is a Christian country, Merry Christmas, not Happy Holidays!" In 2017 the argument against Islamic immigration is that Muslims are a threat to secularism, to women's rights, and to gay rights. An irreligious man who typically votes Democrat will ignore the former argument but might be worried about the latter.
Transgender bathrooms. Trump said that transgender people can use whatever bathrooms they want. I think it's safe to say that the majority of Republicans along with many Democrats and independents, disagree with Trump (see Houston). Compare this with how Republicans reacted to the legalization of SSM in Massachusetts in 2004. Republicans made gay marriage a central campaign issue and it probably got Bush reelected. Furthermore, in 2004 the Republicans used social issues to appeal to minorities and immigrants. This is a significant change.
I disagree with this part. Sure, America is becoming more secular in a formal and broader sense, but that doesn't necessarily mean that individual beliefs - whether the motivation still is overtly religious or not - aren't rooted in them. With that being said, your average Trump Democrat doesn't fit the demographic profile to be swayed by an argument of, essentially, "you're a noble social warrior: you don't want those Muslims taking away our hard-fought social progressive values, do you?". This was a clever act of concern-trolling by Trump and the GOP during the campaign, but I highly doubt it had any real effect. Short of Bill Maher, the only place you saw this argument being used by the masses was in right-wing blog comment sections. If they were motivated by a message rooted effectively in religious bigotry, then it's coming from the same place and striking the same chords as it did 10-15 years ago. If it didn't get them then, then it wouldn't have gotten them now, and especially in a less naturally potent context.
Which brings me to this: there are still religious people in the Democratic Party. Hard to believe for some, I know! But the fact is that there were and are plenty of people who have been voting Democratic for years that could have just as easily voted for Bush due to his gay marriage-bashing in 2004, but had different priorities and therefore voted for Kerry (and/or Obama). Sixty percent of the country opposed gay marriage in 2004; Kerry got 48% of the vote. You can't just pretend those people didn't (or don't) exist. Nevertheless, the types that eluded Bush in 2004 - of all years - weren't likely to be swayed by an even further leftist message rooting along those lines 10-15 years later...because any message ranting and raving against other religious groups is ultimately only going to be potent if it's coming from an evangelical or far-right position, which Trump didn't use (at least bluntly).
My main point here is that the people who would be susceptible to this kind of message would have been susceptible in 2004; if they didn't fall then, they didn't fall in 2016...or at least for this reason. It doesn't appear that the loss in 2016 was caused by a return to 2004 voting habits (look at where we fumbled).
However, the people who are more likely to be in that religious Democratic category are also more likely to be in a situation where their economic fortunes have faltered. While the country as an aggregate continues to improve, there are obviously rather large subsets of the population that have only seen their fortunes consistently decline since 2008. If you break apart the country into two groups - those who have improved or are holding steady for the past decade versus those who are sinking - I think the trend becomes clear. I think there is considerable overlap between the types who might harbor anti-Muslim sentiment (or pro-religious sentiment) and those who are hurting financially.
Trump embodied the agent of change in a world where they're only hurting more from year to year, and he said the right things to grab these otherwise pretty reliable Democrats - who up until now have been more than willing to overlook their religious concerns for economic ones. Because of that, I don't think 2016 was a "change election" for them in a real sense: they were still voting what they considered to be best for their wallets and pocketbooks. It just happened to involve voting for another party this time.
Additionally, Democrats have to realize that we've likely had a lot of GOP voters "on loan" for the past couple of elections. Obama was able to cut heavily into specific segments of the prior-GOP coalition and use it to (mostly his own) advantage in both 2008 and 2012. Sure, there are sizable chunks of this group that still remain with us - especially in suburban areas - but when you look at the Midwest in particular (2004-2016), it's pretty clear that enough of them reverted in places where it mattered.
It's easy to understand why Democrats assumed they had the upper hand, because generally, if you can lock down specific segments of voters for multiple elections, they tend to stay with you. However, this may have been more of an issue relating specifically to Obama as an individual and the caliber of GOP candidates he faced.
So in short: these religious voters didn't defect to the GOP because Trump sold them a socially-progressive message of religious bigotry. They would be more likely to respond to a Bush-era one if anything - because that is the root of such sentiment - but the real root of their behavior is locked in their economic fortunes. They defected because they felt Trump was the better economic choice in a world where the status quo has seen their fortunes consistently decline, and they're tired of it. Additionally, Democrats were too generous in their assumption that many of these voters (and others) were locked into our column after the wins in 2008 and 2012, failing to realize that a sizable chunk of Obama voters were in fact more likely to vote for GOP candidates - as they had been doing prior to his arrival - than they could have imagined.
