I think it's pretty safe to assume that he's the one benefitting the most from the lack of fact checking.
Not safe at all. (Covington Kids, for one thing.) The groupthink among the left-leaning media, particularly the news, is pretty egregious. The degree to which they communicate with each other using electronic networks and create their thought bubbles is well documented at this point. If you "follow the money," to figure out who benefits, then it turns out, it's Far Left activists who benefit by getting to push their agenda and set the narratives. This even results in monetary benefit through fundraising.
That's what I meant by "benefitting the most". You might dismiss it as the left-leaning media you mentioned, but this should be a good starting point to keep track of Trump's false claims: https://www.washingtonpost.com/graphics/politics/trump-claim...