It is not one or the other...there is a demographic change. We also have to get our side to the polls. You are correct in that the difference here could easily have been getting our vote out.
Either way, the demographic change has caused us to just barely scrape by when we do win. 2000 was a popular vote loss, and 2004 was too close considering that we pretty much peaked our GOTV in that cycle. The big difference is that the left now has their machine in place in every swing state to get all these groups to the polls. It is baked in now every presidential cycle.
The answer is the big red machine isn't in place, and has no idea what demographics are about ~ I think they belive it's all about the mexicans ~ but really it's more about the relative death rates to an even greater degree.
White folks live longer than black folks, and people from El Salvador live longer than everybody ~ which is weird, since they don't down home ~ just here in America ~ dude's live LONGER and we have so many of them in Fairfax County they've actually affected our county average life expectancy ~ we all live longer, on average, than anybody else in America. It's up there with the Swedes!
So, you go out to register 1000 black Democrats today, 4 years from now you'll probably need to replace a whole big bunch of 'em. If they were 1000 white Democrats, several dozen more would still be around and your replacement costs for new registrants would be minimal (meaning, as low cost as its going to get). The Salvadorans are mostly on parole so they don't count anyway.
We have plenty of surplus white people out there who can be rounded up, registered, and sent to the voting booths to do their duty on election day. Just a matter of having the will to do it. This last candidate apparently didn't believe in that sort of thing.