Why did Oklahoma reject Clinton in 2016 and Sanders in 2020 after voting solidly for them the previous cycle?
They represented different things + the electorate changed.
2008: Clinton was the more culturally conservative, WWC-seeming candidate. She ran a more economically populist, culturally moderate campaign than Obama or her 2016 iteration. It's easy to forget that Hillary Clinton won impressive margins in upstate rural NY in her Senate races and put a special focus on the region.
2012 (yes): Barack Obama only got 57% of the vote and lost a number of counties to pro-life activist Randall Terry and local gadfly Jim Rogers. Rejection of the Democratic Party/Obama admin by remaining registered Dems who likely voted Republican in the general.
2016: Clinton by 2016 became the Democratic elite candidate and shifted away from her previous orientation. It's apparent even in her announcement video that she discarded the 2008 message for a more cosmopolitan, social liberal one. There were fewer registered Dems by 2016 than 2008, and those Dixiecrats who remained simply voted Sanders as a rejection of Hillary Clinton, who had been demonized by conservative media and was loathed in red America.
2020: Even fewer Dixiecrats were around, leaving a less protest-y electorate. Plus, Biden simply didn't inspire the vitriol that Clinton did. He was seen as the more conservative candidate and didn't have Hillary's baggage. By 2020, Sanders was more culturally leftist too, which can't have helped.
