Imagine if the justice department were not controlled by an appointee of the President, but by someone who wins a national election for US Attorney General. We have elected state attorney generals, district attorneys, etc. Under this scenario, the attorney general would be elected in the midterm elections.
2018 would have been an opportunity for Democratic former prosecutors to build a national campaign. I’m not sure Harris would be able to run as a second-year Senator (although she could have skipped the Senate to run for this office.) It could also be Klobuchar, although there would also be the question of how her abusiveness to her staff could be problematic.
We probably would have a different Trump administration if he knew that the Attorney General wasn’t his man (although we might not have a President Trump if Christie had dodged Bridgegate by running for US Attorney General in 2014 rather than for a second term as Governor.) We would also have a sense of how vulnerable an incumbent is on the electoral college math. If the 2018 Democratic nominee for attorney general won the major swing states, Democrats could be rather confident. If a Republican nominee lost the popular vote, but kept Wisconsin and Florida, it would be a different story.