Largest margin a party has won a state, only for it to be won by the opposing party next election?

[TheReckoning]

Nixon won Mississippi in 1972 by 58.6 points. It voted for Carter the next election.

Is this the largest one?

[𝕭𝖆𝖕𝖙𝖎𝖘𝖙𝖆 𝕸𝖎𝖓𝖔𝖑𝖆]

Barry Goldwater (R) won Mississippi by 74 points in 1964, and the state voted for George Wallace (American Party) in 1968.

Even more, Franklin Delano Roosevelt (D) won South Carolina by 80 points and Mississippi by 87 points in 1944, and both states voted for Strom Thurmond (States' Rights/"Dixiecrats") in 1948, but Thurmond appeared on the ballot as the official Democratic candidate in those states, so I am not sure it counts.

Counting only major parties, I found that William Jennings Bryan (D) won Utah by 65.5 points in 1896, but the state voted for William McKinley (R) in 1900.

[If my soul was made of stone]

Georgia went from Nixon+45 in '72 to Carter+34 in '76. While these individual margins aren't as impressive as those mentioned earlier in the thread, they're up there in terms of electoral feats for the fact that both swept all of the state's 159 counties, Nixon making significant inroads into the Black Belt and Carter in the Unionist Appalachian north.

[TheReckoning]

Georgia went from Nixon+45 in '72 to Carter+34 in '76. While these individual margins aren't as impressive as those mentioned earlier in the thread, they're up there in terms of electoral feats for the fact that both swept all of the state's 159 counties, Nixon making significant inroads into the Black Belt and Carter in the Unionist Appalachian north.

Nixon won GA by 50 points

[DistingFlyer]

If we look at regions, the South's 38% margin for Nixon in 1972 being turned into a 9% margin for Carter would probably take the top prize - it also has the distinction of the safest region for one party being turned into the safest for the other party.

If you want to go the other way (biggest margin from being won by the other party), Roosevelt's 45% lead in the South in 1932 was previously a 7% lead for Hoover in 1928.

[Chips]

In this decade? Bush's 21 point 2004 win in Indiana followed by Obama's win.