“USA 1980 and USA 2016 are demographically completely different countries.”
Yes, but several of the factors that were in place during the Reagan election are in place again, including fear for national security, a sense of wanting to rekindle national pride after getting embarrassed (e.g. Iran taking Americans as hostages), and a prolonged period of economic malaise.
If Trump stops the unforced errors, particularly his personal fights involving women, and stays focused on borders/jobs - he might have a chance.
He needs to hold almost all of GWB’s states picking up a rust belt state or two (MI? WI?) to make up for some Hispanic-driven losses (CO, NM) from the GWB slate. FL should be a big worry. Hillary got slightly more votes than he did in the primary and she will inherit all of Bernie’s votes, while Trump is less certain of picking up all of Cruz/Rubio’s. Virginia is going to very tough too.