1948: The whole Truman victory was a shock, but maybe the closeness of New York? Dewey did end up winning it, but by less than 1% margin in a state where he was the popular second-term governor.
1952: None, really
1956: Louisiana. It went from a D+6 state to R+14 in an election that didn't really have significant swings, and the rest of the deep south held pretty firm for Stevenson.
1960: Hawaii being decided by 115 votes.
1964: Mississippi. Not that Goldwater won it, but that he got a 74 point margin. The GOP went from winning around 75,000 votes (25%) to around 360,000 (87%). You'd think there would be a little more residual Democratic vote, right?
1968: Texas.
1972: Massachusetts going for McGovern, and not by a particularly close margin.
1976: I'll break the rules here: the demographic breakdowns. Young people were split even between Carter and Ford, and women voted the same way as men. This is a very rare situation, at least in a non-landslide election. Young people and women have always leaned left in modern American politics, and while Carter was seen as a religious southern democrat, he definitely campaigned to the left of Ford. So this surprises me.
1980: Arkansas.
1984: Minnesota. I know this is a home-state advantage thing, but still. This was an election where Massachusetts, Rhode Island, and Maryland voted for the GOP.
1988: Pennsylvania. Considering how the nation as a whole trended heavily D from 1984 (not enough for a Dukakis win, but still), you'd think he would have won Pennsylvania. Pennsylvania used to be to the left of the nation back then, and Bush doesn't seem like a particularly good fit.
1992: New Hampshire. It was Bush's second-strongest state in 1988. Even with Clinton's move to the centre and the northeast becoming a D region, it's still impressive.
1996: Arizona. Need I say more?
2000: West Virginia. Not too surprising in hindsight, but at the time, West Virginia was one of the strongest Democratic states in the nation.
2004: Wisconsin. Kerry got a narrowly better margin there than Gore, despite the nation as a whole swinging to the right. Considering Bush made a real play for Wisconsin, it's surprising he was unable to pull it off.
2008: Indiana, obviously. Virginia voting D+6.3 was a surprise at the time, although in hindsight it shouldn't be. But Indiana voting for a liberal Democrat was a complete shock.
2012: Florida, although there were no real big shocks in this one.
2016: PA, MI, and WI are the obvious ones, but I'll actually go for Iowa and Ohio. Not that Trump won them, but the sheer margins. Ohio had long been a bellwether, usually only 2-3 points to the right of the nation, and suddenly it had a 10pt GOP lean. Iowa was, if anything, a lean D state since the 1980s, and suddenly it was voting to the right of Texas. Pretty crazy shifts.
2020: The consensus here seems to be GA, which I agree with. But just to switch it up, I'll actually go with Florida. It went from voting 3pts to the right of the nation, to 8pts. Trump had a net gain in Miami-Dade of around 200,000 votes. I certainly didn't expect Florida to vote to the right of Georgia.
Elections in Mississippi in that era were explicitly and openly rigged. I don't know that anyone was surprised when the county machines threw it to the anti-civil rights candidate in a landslide? They just happened to have a different letter after their name that time.
