Let's talk about 2020

[Skill and Chance]

If the 2020 map is the 272 EV Dem win with CO, it could be a very substantial PV win for the Republican with further migration south and west during the decade.  Something to keep in mind is that an election year ending in 0 is by far the most likely time for the electoral college to do something weird (although ironically Gore would have gotten even fewer EV on the 2004 map).   

[Skill and Chance]

1968 and 1976 were very close despite anti-incumbent years.

Reagan was fairly, but not "massively" popular during the 1988 election year.

 2000 was pretty pro-incumbent, but ended up being ridiculously close. I wonder if Gore were a little more exciting, would he have had a mildly comfortable victory?

Yes, Gore in 2000 is the most obvious case of a candidate underperforming the fundamentals.  1976 being close was consistent with the economy of the time, but when you add in Watergate, I agree it's surprising Carter didn't do better and that should have been a warning sign for him.  1968 is a case of a very good economy with an incredibly unpopular war at the same time, so I guess they basically cancelled out.  It also wasn't nearly as close in the electoral college.  It also looks like Obama underperformed the fundamentals in 2008 on the surface, but that might just be both parties now having higher floors.

[Skill and Chance]

1968 and 1976 were very close despite anti-incumbent years.

Reagan was fairly, but not "massively" popular during the 1988 election year.

 2000 was pretty pro-incumbent, but ended up being ridiculously close. I wonder if Gore were a little more exciting, would he have had a mildly comfortable victory?

Yes, Gore in 2000 is the most obvious case of a candidate underperforming the fundamentals.  1976 being close was consistent with the economy of the time, but when you add in Watergate, I agree it's surprising Carter didn't do better and that should have been a warning sign for him.  1968 is a case of a very good economy with an incredibly unpopular war at the same time, so I guess they basically cancelled out.  It also wasn't nearly as close in the electoral college.  It also looks like Obama underperformed the fundamentals in 2008 on the surface, but that might just be both parties now having higher floors.

Some people would say Obama overperformed in 2008 because of the economic meltdown. My guess is that he would've won anyway, but I think the huge economic downturn made certain states closer, plus wins in Florida, North Carolina and Indiana.

He certainly overperformed a no financial crisis scenario, but based on history, the incumbent party should be near 40% of the PV with the economy that bad.  Instead, McCain got over 45%.  So the operative question is more why Obama didn't win 40 states in 2008.