The first I saw was during the 2016 primaries. The Democrats cheated and colluded with the media to keep Sanders out and heavily promote Trump. The Republicans cheated in similar ways as the Democrats, but far less flagrantly, relying mostly upon the machines (the Democrats used the machines but also procedural cheats. In the general election, some places in swing state cheated for Hillary but it wasn't enough (they did manage to get the number of Democratic voters higher in order to make the even more fraudulent 2020 results appear less so.