Did the losing party over perform or under perform electorally in each election

[Hydera]

In '68 the Dems overperformed, Humphrey shouldn't have made it that close, with the war and LBJ.
In '72 they underperforned but it was mainly in nominating McGovern and with Eagleton.
In '76 Carter should've won 400+ EVs.
In '88 we should've won much more, if not the election.
In '08, the GOP overperformed, Obama should have won around 400 EVs with the economy as it was.
The rest were pretty much what could be expected.

 
The GOP over performed and prevented Obama from getting 400+ EV's because their vote was pretty resilient. Losing only three million voters while had it been in the past Obama would had won 10%+ and 400+ EV's easily.

[Hydera]

'68: Over
'72: Under
'76: Under
'80: Under
'84: About the Same
'88: Under
'92: Under
'96: Under [albeit Perot was the true over-performer here]
2000: Over
'04: Over
'08: Over
'12: Under
'16: Under

Why


With how good the shape of the country was in 2000, Democrats should have easily won that election, and in 2016 the conditions favored the Republicans.

http://www.cbsnews.com/campaign2000results/state/poll_usop-.html

Lots of things happened. The Perot voters in 1996 split 62% for Bush, 25% for Gore, 7% for Nader, 2% for Buchanan. Most of the reasons is a combination of Religious views because Bush was evangelical, a lot of the 1988 HW Bush/Perot/Perot voters being conservative and finally went back home to the GOP, tax cuts, Perot endorsing Bush, Lewinsky scandal).  

Gore getting 7% of the Dole vote but Bush getting 13% of the Clinton vote due to Lewinsky and the restart of the rural-urban divide on social issues especially with the Lewinsky scandal offending a lot of Christians who voted for Clinton twice.  Most of Gore's dole voters who switched were particularly from the 'burbs who liked how the economy was doing and might as had been uneasy about Bush's evangelicalism.

And Finally mass voter registration of Evangelicals in 2000 that continued into 2004. Due to Bush being an evangelical.