This may sound like a dumb idea at first but hear me out: While it would be a stupid idea to reset the progress in the main campaign, as you could just replay the missions over and over and they would be the exact same, other creators might create campaigns where maps may differ based on decisions made earlier (through campaign flags). In that case, a single map may differ greatly from player to player. For people who notice this and get curious, right now (as far as I know), there are no ways for that player to retry. To my knowledge, you can't even delete and re download. It could just be a simple button in the pause screen, similar to the one in the campaign editor. Of course, a couple warnings after pressing it would be required. Ok, I was wrong. You can indeed delete campaigns and maps you've downloaded but my point still stands.