https://en.wikipedia.org/wiki/List_of_presidents_of_the_United_States_by_previous_experience
20 former Govenors. (Although only 17 were State Governors. 2 were Territorial Governors and 1 was a Military Governor)
18 former Senators. One was a Senator after being President. Maybe this can be AOC's path.
32 with prior military experience.
Only one with no prior military or government experience. (Guess Who?)
Progressives also have to realize that their candidates won't magically win in every district. Still, every primary needs to be contested, if for no other reason than to let the eventual winner know what their constituents value.
I don't think there is really a loser in a primary. The candidate that loses the election learns a bit about the people in their district, and about themselves, which they can take into the next campaign. In fact, I can make an argument that Democrats are in such dire straits right now because they don't have enough candidates losing primaries, and learning from that. That leads directly to weaker candidates in the General Election