2012. A lot of Working class Whites in the Rust Belt are going to abandon Trump as thus far he's trying to govern as a run of the mill Republican and has thus far proved to be incompetent. Iif the Democrats nominate an economic populist, I can see some of the McCain/Romney/Clinton voters going third party or reluctantly backing Trump.
If they nominate someone like Biden, Harris, or Klobuchar, I can see a sort of hybrid scenario happening, in which Dems win back MI, PA, and probably WI, but also win FL, NC, AZ and maybe GA.