I'm not sure how exactly the campaign counts difficulty completion. Rather than choosing the difficulty for the entire campaign, you choose the difficulty for individual missions, as seen below. In that screenshot, I've completed the first 3 missions in the campaign on Easy. If I were to switch to Medium for one mission, what would happen when I finish the campaign? Will it take the majority of missions I've completed on a certain difficulty?
In the medal section, there's a series of medals from bronze to gold for completing all campaign missions. If I complete the campaign on Medium, will I be rewarded the silver Medium medal and the bronze Easy medal, or will I have to do a separate playthrough on Easy?
I can't find anywhere ingame where it explains how exactly the difficulty works in regards to overall campaign progress and medal awards.