Shoshone County, ID in 1976

[Vosem]

Carter was generally very weak in the Mountain West. Labor unions also trended left during the 1980s; Carter won union members and their households 59-39 on his way to a 2-point victory in 1976, while Dukakis won them 57-43 on his way to a 7-point defeat in 1988.

Actually, the history of the union vote is sort of fascinating; this one was one of the first questions to be asked in exit polls, and Wikipedia has 'union vote' (including union members' households) statistics going back to 1960. Here's that information (the number in parentheses is lean relative to national vote):
1960: Kennedy 65-35 (D+30)
1964: Johnson 73-27 (D+24)
1968: Humphrey 61-29-10 (D+32)
1972: McGovern 50-48 (D+25)
1976: Carter 59-39 (D+18)
1980: Carter 48-45 (D+13)
1984: Mondale 54-46 (D+26)
1988: Dukakis 57-43 (D+21)
1992: Clinton 55-24-21 (D+26)
1996: Clinton 60-30 (D+22)
2000: Gore 59-37 (D+22)
2004: Kerry 59-40 (D+22)
2008: Obama 59-39 (D+13)
2012: Obama 58-40 (D+14)
2016: Clinton 51-43 (D+6)
2020: Biden 56-40 (D+12)

Before the Obama era, which featured a general trend of union members well to the right of where they had been earlier, the weakest Democrat among union voters, relative to national performance, was Carter in both of his elections.