'easily' is doing a lot of heavy lifting there. As an American who maintains multiple friendships all over the political map due to significant nonpolitical shared interests, I've got more perspective on that commotion.
While it's true Trump won with Russia's help both times, it took an extraordinary effort with extraordinary results, patterned after internal Russian political manipulation (so it's not like it was just made up haphazardly). It required attentive siloing of Americans into camps isolated from each others' worldviews and the concealment of what the other camp was seeing. This is not remotely 'easy manipulation', it's lengthy hard work requiring great effort and attention, toward a goal of confusing both sides against each other, and eventually removing the very concept of reality.
Sounds impossible, but it works… at least to the extent of getting results, and tearing apart a country. That's why 'civil war' is constantly invoked by these forces: you can't do anything constructive this way but the goal is to spur internal conflict.
That's why it's relevant that it's foreign interference: the interferer isn't hobbled by a need to survive in the resulting damaged country. They can do whatever they want, because they're doing it to an enemy.