If the GOP is supposedly dying, it doesn't explain how the Dems utterly failed to notice what was happening for decades where they were contracting to the urban/suburban areas.
Even if demographics are moving towards the Dems, it doesn't help if they screw themselves up.
I don't think they failed to notice that. You just can't hold on to 100% of the US population as a political party. The Republicans achieved it once, with the Southern Strategy, but all it resulted was them trading their original base for a new one.
As a democrat, I've always thought the "dems are losers" stuff has been pretty exaggerated. I mean its US politics, on average you're going to win about half the time. What I would say is that the democrats are coming unglued a little. When Bill Clinton made the party take a sharp turn to the right, he created a huge faction of moderate democrats, which AFAIK is the dominant faction among baby boomers (which also makes them the largest blue voting bloc since old people vote more). If someone over the age of 60 uses words like "socially liberal, economically conservative," to describe themselves, they're probably from that bloc. These voters typically lean left on some issues and right on others, and have a lot of overlap with older swing state independents and the "fiscally conservative" Republicans. On average they don't hate Republicans, but like those other groups they're disappointed that religious fundamentalists, who they're apathetic at best to, are being pandered to over them. Because this faction fondly remembers Bill, this was Hillary's base. (side note, this is why its so bizarre to me that she underperformed in swing states but matched expectations in both blue and red states, I've never seen a convincing explanation for that)
Contrasting that is the younger generation, me. We were Bernie's base. We're blue on almost all issues (for me, the gateway drug to this was being angry about post-9/11 culture and Iraq), we're angry about capitalism and the 1%. We feel that the current leadership is weak. Young blue voters and young red voters both share an anger that we've been denied something that was promised to us*, which was the Trump-Bernie connection (which was overstated but still there). The thing about young democrats compared to old democrats is that older democrats aren't actually that horrified by most things that Republicans do. My mom is a blue voter, for example, but she's also over 60. That means she grew up in segregation. She doesn't begrudge LGBT people or racial minorities their rights, but its not a voting issue for her at all. She loved Clinton and thinks liberals can't handle the economy, so to her things like the government shutdown read vaguely like justice. She hates the idea of raising taxes. In a lot of ways, she's a lifetime democrat who could take two steps to the right, trip and full and suddenly be voting Republican every year.
My generation doesn't think like that at all. To us, things like the government shutdown, the Iraq war justification mishaps, the immigration ban, stuff like that, these are sins that need to be punished. A party that would do those things, and stand behind its decisions at a later date, doesn't deserve to exist. And this is the disconnect in the democratic party, how we interact with the republican party. Older democrats think that republicans should be dealt with mildly and with a lot of cooperation. To them, the polarization of politics, the rise of Trump and the religious right, that's scary. But the actual things Trump and the religious right do, eh, I mean its bad but that's just their political view and it has to be respected**. To me that just reads as incredibly weak.
A great example of this is environmentalism. Ask a democrat over 45 years of age, you'll either get apathy, straight climate change denial, or "I believe in it but if someone else doesn't that's fine." Not so for young democrats. If I saw a democratic politician get up, say that climate change is a fact, and proceed with five minutes of creative insults for climate change deniers, I would cheer in real life. So of course the democratic leadership, both composed of and pandering to the moderate bloc, feels hopelessly weak to me and other millennials. To us, it seems like if our elected politicians would stand up, all as one, and get real mad about climate change deniers and the right to abortion and everything that Republican politicians get mad about, we could push the Republicans aside in a second. It reads like the party is afraid that no one will like their liberal beliefs, so they hide behind being non-threatening instead of arguing passionately for their beliefs. But our party leadership isn't dumb, they know that the Clinton democrats are their big vote mine, and they are actually trying to shift left. And indeed look at Hillary, she went hella left to try and draw Bernie's base over. So like I'm not happy with the democrats, my main complaint basically boils down to "keep doing that thing that you're doing, but with feeling this time."
*note: we emotionally
feel we've been denied something promised to us. That's not our actual political view, and everyone my age would have a different answer for what we lost and who took it away from us. Some might think all that talk is being entitled. But the core anger is near universal, especially among young white men (which is why most of the alt-right is young white men, drawn in by conspiracy theories that its women or immigrants that have cost them their place in the universe).
**this is why Hillary's "basket of deplorables" comment really hurt her, because it horrified the older democrats that formed her base. I guarantee you that it hurt her far less amongst Bernie supporters, because while it was ultimately an immature thing to say to a lot of younger democrats it would read as an accurate summary of Trump's base.